JPH06143665A - Pseudo multi-gradational electrostatic recording apparatus - Google Patents

Abstract

PURPOSE:To provide a pseudo multi-gradational electrostatic recording apparatus which can prevent the generation of the density irregularity of an image at a plastered part of the gradation image and record the image with a high quality at all times. CONSTITUTION:A gradation correcting circuit 35 is provided between a gradational original image signal receiving circuit 31 and a pseudo multi-gradation converting circuit 32. An image signal fed from the gradational original image signal receiving circuit 31 is converted to a pseudo multi-gradation by the gradation correcting circuit 35, so that the pattern of the density irregularity of a middle density area where the density irregularity is conspicuous when the image is printed is negated. The recording apparatus is adapted to make corrections of the gradation as above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pseudo multi-gradation electrostatic recording device for recording a pseudo multi-gradation image on electrostatic recording paper using a multi-stylus electrostatic recording head.

[0002]

2. Description of the Related Art Conventionally, in an electrostatic recording apparatus such as an electrostatic plotter, an electrostatic latent image is formed on a recording sheet by, for example, a multi-stylus electrostatic recording head, and a wet developer is attached to the electrostatic latent image to form a toner image. An apparatus using a multi-stylus electrostatic recording method for forming is widely put into practical use. In particular, A
As a color printing apparatus for performing large-screen printing of 0, A1, etc., an apparatus adopting the above method, which has a high printing speed and can simplify the apparatus configuration, is most often used.

By the way, conventionally, the electrostatic plotter has been mainly used to print a line drawing. However, with the spread of computer graphics in recent years, it is possible to print an image or a gradation image having a large halftone painting area. It is being used more often. On the other hand, the printing by the multi-stylus electrostatic recording method described above performs binary recording depending on the presence or absence of recording dots, and gradation expression cannot be performed by the recording dots themselves. Therefore, when gradation expression is performed by the multi-stylus electrostatic recording method, the multi-gradation original image signal is replaced with a binary dot distribution density change by pseudo multi-gradation conversion before printing. An example of a pseudo multi-gradation electrostatic recording device using such a multi-stylus electrostatic recording system is shown in FIG.

In FIG. 1, this pseudo multi-gradation electrostatic recording device comprises an electrostatic recording paper roll 1 on which electrostatic recording paper is wound,
Multi-stylus electrostatic recording head 2 and image signal processing unit 3
, Developing head 4, guide roller 5, pressure contact roller 6
A transport roller 7 and a pinch roller 8.
Further, the image signal processing unit 3 includes a gradation original image signal receiving circuit 31, a pseudo multi-gradation conversion circuit 32, a matrix distribution circuit 33,
A printhead driver circuit 34. The multi-stylus electrostatic recording head 2 includes an image signal processing unit 3
An electrostatic latent image is formed on the electrostatic recording paper 9 in accordance with a predetermined image signal supplied from. The developing head 3 adheres toner to the electrostatic latent image formed by the multi-stylus electrostatic recording head 2 to develop it as a toner image. Further, the transport roller 7 is for unwinding the electrostatic recording paper 9 from the electrostatic recording paper roll 1 by rotation.

The electrostatic recording paper 9 pulled out from the electrostatic recording paper roll 1 is guided to the conveying roller 7 through the multi-stylus electrostatic recording head 2 and the developing head 3. Further, the pressure contact roller 6 is arranged so as to face the multi-stylus electrostatic recording head 2 via the conveying path of the electrostatic recording paper 9, and the print head 2a of the multi-stylus electrostatic recording head 2 is provided with a surface of the electrostatic recording paper. Are pressed against each other.

FIGS. 9A and 9B are views showing cross-sectional structures of typical print heads. Of these, the print head of (a) is of the same-surface control type, in which a plurality of recording needles 11 are arranged in a row along the main scanning direction and a plurality of auxiliary electrodes 12a and 12b are provided on both sides thereof. Deploy. Both the recording needle 11 and the auxiliary electrodes 12a and 12b are encapsulated in an insulating resin, and only one end surface of the electrostatic recording paper 9 in contact with the recording needle 11 is exposed. The print head shown in FIG. 3B is of a double-sided control type, and as shown in the figure, an auxiliary electrode 14 is provided at a position facing the recording needle 13 with the electrostatic recording paper 9 sandwiched therebetween.

FIG. 9C is a diagram showing the arrangement and connection of the recording needles and the arrangement of auxiliary electrodes. In the figure, the recording needle is divided into every other blocks (A1, B1, A2, B2, ...) A and B in units of a predetermined number, and the blocks are not adjacent to each other, that is, A blocks or B blocks.
The recording needles of the same order among the blocks are commonly connected to form a matrix wiring. Further, a plurality of control electrodes (auxiliary electrodes) C-1, C-2, ... Are arranged so as to extend over half of each block.

When recording is started, an image signal having gradation information for each pixel, which is sent from a host device (not shown), is taken in by the original gradation image signal receiving circuit 31, and is then transferred to the pseudo multi-tone converting circuit 32. Supplied. The image signal input to the pseudo multi-gradation conversion circuit 32 is converted into a binary signal by a pseudo multi-gradation conversion method based on various algorithms such as a density pattern method, a dither method and an error diffusion method. The binarized image signal is input to the matrix distribution circuit 33. The matrix distribution circuit 33 is a memory so as to be adapted to the matrix drive of the print head 2a, or when the recording needles have a two-row array structure in a zigzag pattern, to output image signals in an order compatible with the array. Change the read address and timing from. The print head driver circuit 34 includes the matrix distribution circuit 33.
An electrostatic latent image is formed on the electrostatic recording paper 9 by successively energizing the recording needles and the control electrodes according to the image signal supplied from.

That is, the print head driver circuit 3
From 4 a drive signal corresponding to the print image signal is applied to the recording needle of either the A block or the B block, and at this time, the control electrodes straddling the blocks for printing with the print image signal are applied. A pulse voltage is applied. The voltage applied to the recording needle and the control electrode is set to about half of the voltage required for recording. In this example, the control electrode is + 300V, and the recording needle is-
300V is applied to each.

In the recording paper conductive layer near the control electrode to which the pulse voltage is applied, as shown in (a) or (b) of FIG. 9, a charge having the same polarity as the voltage applied to the control electrode, that is, a positive charge. Is induced by capacitive coupling. Then, by the action of the electric field created by this positive charge and the voltage applied to the recording needle, the charge moves from the recording needle to the surface of the recording paper to form an electrostatic latent image. The electrostatic recording paper 9 has a two-layer structure in which a dielectric recording layer is formed on the surface of a conductive-treated sheet,
At the time of recording, it is unwound from the roll 1 as the transport roller 7 rotates. The electrostatic latent image formed on the dielectric recording layer by the electrostatic recording head 2 is developed as a toner image by wet development by the developing head 4.

In this way, the position corresponding to the electrostatic latent image is sequentially designated by the voltage application to the control electrode, and the voltage corresponding to the pattern of the electrostatic latent image is applied to the recording needle. Then, the recording positions are arranged in order, and when the formation of the electrostatic latent image corresponding to one main scanning line is completed, the electrostatic recording paper 9 is moved in the sub-scanning direction by one dot to move to the next position. Start printing the line.

[0012]

As described above, when a gradation image is recorded using the multi-stylus electrostatic recording head, first, a voltage which is about half the voltage required for recording is applied to the auxiliary electrode. Then, an electric charge is induced on the recording paper by capacitive coupling by the applied voltage.
This induced charge decays with time, and when the voltage application to the auxiliary electrode is cut off, this decay remains as a reverse polarity charge in the recording paper conductive layer. Then, if the next voltage is applied before the residual charges are dissipated, the increase in potential is hindered by the amount of the residual charges and the print density is reduced.
Further, since the residual charges move in the horizontal direction through the conductive layer of the recording paper, the charge distribution changes in a complicated manner depending on the order and timing of blocks in the peripheral portion. As a result, uneven distribution occurs even in one block, and in this case, uneven image density called block density unevenness occurs. FIG. 8B shows a typical block density unevenness. As shown in the figure, when all dots are solidly printed, sawtooth-like density unevenness occurs on the recording paper.

These density irregularities are practically almost problematic in applications mainly for printing line images by improving the prescription of electrostatic recording paper or devising the order of block designation. It has been improved to the extent that it does not happen. However, when a filled image is printed, there is a problem that density unevenness still remains as a long strip-shaped periodic pattern in the sub-scanning direction.
For example, when a computer graphics image including an intermediate gradation or a multi-gradation natural image is converted into a pseudo multi-gradation and printed, the shaded portion of the intermediate gradation is the most noticeable density unevenness. Moreover, the present inventor has found that the pattern of density unevenness in the filled portion of the intermediate gradation is different from the pattern of density unevenness in the solid print portion.

Generally, in a printer using a multi-element head such as a thermal printer or an LED electrophotographic printer, the image density can be easily changed by changing the voltage applied to the print head.
Thus, the drive voltage and the pulse width are adjusted for each print element or for each block of the drive to prevent density unevenness. However, in the recording apparatus using the multi-stylus electrostatic recording method, the method of changing the voltage is complicated because the recording voltage is high, and the image density hardly changes even if the print pulse width is changed. The above method cannot be an effective solution because of the property that it does not.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pseudo multi-gradation electrostatic recording apparatus capable of preventing image density unevenness in a shaded portion of a gradation image and always recording with good image quality. .

[0016]

In order to achieve the above object, the present invention divides a large number of recording needles arranged in a row in the main scanning direction into blocks by a predetermined number of units, and records of the recording needles belonging to non-adjacent blocks. A matrix-like wiring is formed by commonly connecting those at the same position, and a print head is provided in which auxiliary electrodes are arranged corresponding to the blocks, and a predetermined pseudo multi-gradation conversion is performed for this print head. By supplying a print image signal obtained by binary-converting the multi-tone original image signal by the method, a latent image is formed on the electrostatic recording paper, and the latent image is developed with toner to record a pseudo multi-tone image. In the pseudo multi-gradation electrostatic recording device, the correction characteristic is set according to the image density unevenness generated on the electrostatic recording paper,
According to this correction characteristic, gradation correction means for correcting the gradation of the multi-gradation original image signal is provided.

[0017]

As a result of taking the above-mentioned means, the following effects occur. That is, as a correction characteristic, for example, a correction characteristic for canceling the density unevenness in the intermediate density range is set, and the multi-gradation original image signal is subjected to gradation correction based on this correction characteristic, and then pseudo multi-gradation conversion is performed to perform print head conversion. Since the multi-gradation original image signal is pseudo-multi-gradation converted and printed, the block density unevenness in the intermediate density range where the density unevenness is most noticeable can be effectively suppressed. It is possible to provide a pseudo multi-gradation electrostatic recording device that can perform good printing.

[0018]

1 is a block diagram showing the structure of a pseudo multi-gradation electrostatic recording apparatus according to an embodiment of the present invention. In addition,
In the figure, the same parts as those in FIG. 8A are designated by the same reference numerals. Reference numeral 10 denotes an image signal processing unit, and a gradation correction circuit 35 is provided between the gradation original image signal reception circuit 31 and the pseudo multi-gradation conversion circuit 32. This gradation correction circuit 35
Is for giving a gradation correction described later to the original image signal supplied from the gradation original image signal receiving circuit 31.

FIG. 2A is a diagram for explaining a situation of occurrence of block density unevenness when a pseudo multi-tone conversion image is printed without applying gradation correction. The applied pseudo multi-gradation conversion algorithm is called the error diffusion method, and the error amount generated when the focused image point is quantized to “0” or “1” is dispersed to the peripheral pixels to This is to eliminate the quantization error. This algorithm has excellent gradation difference characteristics, and has the advantage that the edges of the image are sharp and can be expressed with high resolution. In addition, the dot arrangement becomes almost random, and the weights of the dots of each color in the multicolor print are also random, so that moire fringes do not occur, and there is an advantage that there is no deviation in color expression due to the weight of the print dots. is there.

In the printing by the random dot arrangement represented by this algorithm, the block density unevenness becomes the curves shown by S, M and H in shadow, intermediate density and highlight, respectively. Since all dots are printed in the shadow portion,
As shown in (b), it becomes a sawtooth density unevenness pattern having sharp edges. The density unevenness in the intermediate density area has a relatively large density difference and is visually noticeable, but the shape is not a sawtooth pattern, the block boundary is low density, and the center part of the block is high density. The distribution curve is rather smooth. Moreover, the uneven density in the highlight portion is not so noticeable, and the distribution is more gentle. Corresponding to the actual situation of various density unevenness as described above, in the present invention, the correction is performed by giving a correction characteristic for canceling the density unevenness pattern M in the intermediate density region where the density unevenness is most noticeable. b) shows the correction curve.

FIG. 2C is a process explanatory view of the pseudo multi-gradation electrostatic recording apparatus shown in FIG. In the figure,
I is a step of receiving the multi-gradation original image signal, and the original image signal in the intermediate density region to be corrected has a flat characteristic as shown by Ia. This original image signal is subjected to gradation correction in the next gradation correction step II. IIa is a diagram showing a correction characteristic in units of blocks. Since the original image extends over a plurality of blocks of the print head, the correction characteristics IIa of the unit block are expanded into a plurality of blocks in the main scanning direction to perform tone correction. As a result, the original image signal is corrected as shown by IIb, resulting in an image with intentionally unevenness.

The tone-corrected original image signal is converted into a binary image signal by a pseudo multi-tone conversion algorithm such as an error diffusion method in the next pseudo multi-tone conversion step III. Since this conversion is a step of performing binary conversion of the gradation of the original image as faithfully as possible, the gradation characteristics will be described as almost unchanged.

In the next matrix conversion step IV, the binary image signal is converted by combining the memory read address and the timing so as to comply with the print needle arrangement of the print head and the block selection order. Then, this binary image signal is sent to the print head driver circuit 34 in the printing step V. In the printing process V, the block density unevenness as shown in FIG. The density unevenness pattern in the halftone portion where the block density unevenness is most noticeable is Va in unit block units.
The density unevenness occurs in each block. Then, the binary image signal corrected by the correction characteristic indicated by IIa is affected by the density unevenness indicated by Va for each block, and as a result, is returned to the original flat characteristic as indicated by Vb.

As described above, according to the present embodiment, the gradation correction circuit 35 is provided between the gradation original image signal receiving circuit 31 and the pseudo multi-gradation conversion circuit 32, and the received original image signal is pseudo multi-gradation converted. Since gradation correction is performed by providing a correction characteristic that cancels the density unevenness pattern M in the intermediate density area where the density unevenness is most noticeable when an image is printed, the block density unevenness in the intermediate density area is effective. It is possible to obtain a printed image with less unevenness.

In the above description, the gradation correction is shown by focusing on the block density unevenness pattern M in the intermediate density region where the density unevenness is most noticeable, but the same correction is made when correcting the regions other than the intermediate density region. Correct according to the pattern. The designation of the correction amount can be selected in various ways. For example, it is also possible to correct only a specific intermediate density range and not to correct other density ranges. However, in the case where the density areas other than the intermediate density area are also corrected at the same time, the above-described apparatus may cause overcorrection in the shadow portion and the highlight portion. Hereinafter, a method of performing appropriate gradation correction over the entire density region without fear of such excessive correction will be described.

FIG. 3A is a diagram showing a pattern of block density unevenness, in which the amount of unevenness differs from that of the pattern for each gradation level (S, M, H). Then, in order to correct these block density unevenness, the correction curve shown in FIG. This correction curve has the same pattern shape at each density level, but the correction amount is set to be small on the highlight or shadow side and large on the intermediate part. For example, in order to completely correct unevenness in the entire solid image portion, there is no choice but to lighten the dark portion in accordance with the lightest portion. If you correct in this way, you will get an image with insufficient density overall,
Since the adverse effect of the correction occurs, it is better not to apply the correction in the whole solid image part.

For each gradation level, as shown in FIG.
The result of performing the gradation correction according to the correction characteristic shown in (b) is shown in FIG. Since no correction is set in the shadow area, the block density unevenness remains as it is in the printed image as shown by S ', but the unevenness in the shadow area is not so noticeable from the beginning, so there is no problem. Since the correction is set to be perfectly performed in the intermediate density region, a good image without unevenness can be obtained.
In the highlight area, since the shapes of the unevenness pattern and the correction pattern are slightly inconsistent, slight unevenness with a small pitch remains, but the remaining amount of unevenness is significantly reduced. That is, according to this correction method, it is possible to perform the correction with emphasis on the intermediate density where the unevenness is most noticeable, and it is possible to prevent overcorrection on the highlight side or the shadow side where the amount of unevenness is small.

In FIG. 3 (b), a typical density region S,
Although the respective correction characteristics of M and H are shown, the relationship between an arbitrary density region and its correction amount can be obtained from the correction curve shown in FIG. In the figure, the horizontal axis indicates the gradation level of the image signal before correction, and the vertical axis indicates the gradation level of the image signal after correction. In the figure, C is no correction, and C-1 and C-
Reference numerals 2, C + 1 and C + 2 denote correction curves having different correction amounts, and any one of the above curves corresponds to each position in the main scanning direction within one block. For example, in the correction characteristics shown in FIG. 3B, the curve C + 2 is applied to both ends of the block for maximum correction in the direction of increasing the density, and the curve C is applied to the uncorrected portion. Further, the curve C-2 is applied to the central portion of the block so as to give the maximum correction in the density decreasing direction, and the intermediate curve is applied to the intermediate portion.

Thus, the correction patterns are the same,
The correction calculation and the correction table can be simplified by applying the characteristic curve in which only the quantitative parameter changes. Note that the correction curve needs to have a large correction amount in the intermediate density region, but on the highlight or shadow side, it is not always necessary to perform correction over the entire gradation region, and as shown in FIG. As shown, the correction may be limited to the intermediate gradation range.

As described above, in the present embodiment, the correction amount in the gradation correction circuit 35 is set to be small on the highlight or shadow side and large in the middle portion, so that the intermediate density where the density unevenness is most noticeable is set. When a relatively large amount of gradation correction is performed to correct the block density unevenness in the area, the low density or high density area where the unevenness is less conspicuous than the intermediate density area is overcorrected, and the unevenness is increased. Can be prevented.

The above-mentioned electrostatic recording apparatus corrects by paying attention to the density unevenness characteristic in block units of the halftone image which has been subjected to pseudo multi-gradation conversion. Since this block of density unevenness has almost the same unevenness characteristics in each block, the correction characteristics of each block may be unified into a representative pattern and applied to all blocks. However, the block density unevenness changes depending on the block selection order, and there may be extremely small unevenness or a large amount of unevenness in a specific block. Therefore, the present invention can also be implemented by supplementing the correction not to be performed on the block having particularly small unevenness by the designation, or to the correction having the increased correction amount on the block having particularly large unevenness. .

In the electrostatic recording apparatus described above, in order to simplify the gradation correction circuit 35, for example, it is desirable to expand the correction data of a unit block into a plurality of blocks and perform the correction. However, at the end of the electrostatic recording head 2, the block end of the matrix wiring is
If the edge of the effective recording screen does not match the edge of the original image information, there is a problem that proper correction cannot be performed even if the block correction curve is simply expanded from the edge of the original image information and corrected.

In order to solve such a problem, the structure of a pseudo multi-gradation electrostatic recording device is arranged so that the block position of the matrix wiring and the end of the recording screen can be aligned to perform gradation correction. As shown in FIG. In the figure, the image signal processing unit 20 includes a multi-gradation original image signal receiving circuit 31 and a gradation correction circuit 3.
6, a pseudo multi-gradation conversion circuit 37, a matrix conversion circuit 38, a print driver circuit 39, a block correction data circuit 40, and a correction phase position command circuit 41. The block correction data circuit 40 provides a basic correction curve for each block. Further, the correction phase position command circuit 41 gives a command for correcting the non-matching portion between the block position and the effective image end.

The multi-gradation original image signal sent from the host device (not shown) is supplied to the multi-gradation original image signal receiving circuit 31 and stored in the buffer memory or the page memory. This signal is subjected to gradation correction by the gradation correction circuit 36 for block density unevenness. The gradation correction circuit 31 receives an instruction from the block correction data circuit 40 to obtain a correction condition, and also receives a position error between the image end portion and the block end portion of the print head according to an instruction from the correction phase position instruction circuit 41. Take Thus, the gradation-corrected image signal is converted into a binary signal by the pseudo multi-gradation conversion circuit 37 and sent to the print head driver circuit 39 to energize the print head 2a.

The electrostatic recording paper 9 is made by providing a dielectric recording layer on a support sheet that has been subjected to a conductive treatment, and the potential unevenness of the voltage induced in this conductive treatment layer causes the block density unevenness. In the present embodiment, the gradation correction circuit 36 applies gradation correction for correcting the block density unevenness to the original image signal, and the corrected signal is converted into a pseudo multi-gradation signal. The block density unevenness, which is similar to the density unevenness of one block, periodically and sequentially occurs in each block, so basically, a correction curve for one or several types of blocks is created and this correction is performed in the main scan. It may be applied to each block one after another in the direction. The block correction data circuit 40 provides a basic correction curve for each block. Therefore, by making the data that determines the conditions on which the correction is based on such extremely simple small-capacity data, the size and simplification of the circuit can be achieved.

FIG. 5A is a diagram showing the relationship between the block position on the matrix structure of the print head 2a and the print image position. In the figure, E is a recording needle,
The needles at the tip and the end of each block are illustrated by dividing them into blocks A and B of the matrix wiring. C-1, C-2, ... Are auxiliary electrodes, and two auxiliary electrodes are arranged so as to extend half over one recording needle block. The areas indicated by P1 and P2 are print effective screen areas, and the dimensions are such that the multi-gradation original image signals can enter this area without excess or deficiency. When the original image is too large, it is reduced or deleted to a predetermined size, and when the original image is small, it is enlarged or white data is added to the margin, and the signal is treated as data of a predetermined size. P1 and P2 indicate the effective screen area of different devices,
The print effective screen position varies from the block position of the print head such that one device has the screen at the position P1 and another device has the screen at the position P2. Such variations occur due to manufacturing errors and mounting errors of the print head 2a, and manufacturing errors and mounting errors of the recording paper conveyance path. In addition to variations due to such manufacturing errors, the effective screen edge and the block edge may not match at the set position as in the example of P1.

FIG. 5B shows an example of a correction curve per unit block. N in one block
Assuming that there is a book recording needle, the correction characteristic is set so as to suppress the density decrease at the block boundary and to decrease the density at the center of the block. Gradient correction of the original image is performed with the correction characteristics simply combined in the main scanning direction, and P1
If the image is printed on the effective screen, the correction phase shifts by about half of the block size, and the correction acts in the opposite direction to increase the block density unevenness. Therefore, in the apparatus shown in FIG. 4, the non-coincidence portion between the block position and the effective image end is corrected by a command from the correction phase position command circuit 41.

As one embodiment, as shown in FIG. 5 (c), the correction curve at the outermost end is partially deleted, and correction data corresponding to the recording needles 1 to n are created to make the outermost position. Apply. Then, as the correction data of each block following this, the data shown in FIG. 5B is used. The outermost recording needle position 1 to be used is input from the correction phase position command circuit 41, and a correction curve row according to this is generated in the gradation correction circuit 36 to perform correction.

As another embodiment, the correction curve in the unit block as shown in FIG. 5D is cyclically moved in the block. That is, the data of the upper recording needle position is moved to the lower recording needle position by a designated number, and the data deviating from the needle position 1 is returned to the n side. If the data movement distance is l-1, the outermost data is the data of the original l needle position. In this manner, a correction curve string obtained by connecting the correction curves newly created in this way one after another in the main scanning direction is created in the gradation correction circuit 36 and correction is performed. The phase conversion can be performed by instructing the gradation correction circuit 36 from the correction phase position command circuit 41 or by instructing the block correction data circuit 40. Such phase adjustment may be carried out at the stage of assembling the apparatus, and the phase correction amount may be set by a numerical value input means such as a DIP switch or written in the ROM for data input.

As described above, according to the present embodiment, the gradation correction circuit 36 is simplified by correcting the entire screen width in the main scanning direction from the density unevenness correction data of the unit block, and the print head 2a has a matrix shape. It becomes possible to correct the gradation by eliminating the mismatch between the block position of the wiring and the end portion of the print screen and arbitrarily matching the relative positions of the both.

Next, FIG. 6 shows a pseudo multi-gradation electrostatic recording device constructed so as to easily cope with a change in the proper correction amount. Since the proper correction amount corresponds to the block density unevenness, the correction amount must be increased as the unevenness increases. The block density unevenness changes, for example, when the type of recording paper changes. Further, a factor on the apparatus side is that the amount of unevenness differs for each print head. For example, in the matrix configuration of FIG. 9C, if the recording needle block for the control electrode is displaced and deviates from the target position, block density unevenness increases. Therefore, it is preferable that the appropriate correction amount can be changed and set for each device. Further, it is preferable to be able to cope with changes in the type and lot of recording paper, or changes in the appropriate correction amount due to changes in environmental temperature.

The density unevenness is corrected by the correction pattern shape and
It can be handled separately for the correction amount element. When focusing on the block density unevenness in the intermediate density area of the pseudo multi-gradation converted binary image, the density becomes low at the boundary of the block, and the density becomes high at the center of the block. Even if it doesn't change. Therefore, the correction amount for proper correction may be adjustable.

In FIG. 6, reference numeral 42 is a correction pattern shape circuit, and 43 is a correction amount designating circuit. The correction pattern shape circuit 42 stores data representing a correction pattern for each block. In the present embodiment, the correction amount designation circuit 43
Therefore, the correction amount is variable. As described with reference to FIG. 3, C, C-, and C are associated with the respective recording needle positions of the block.
Each correction characteristic of + is applied, but FIG. 3 (b)
If the correction pattern shown in FIG. 4 is fixed and the values of C'-2 and C '+ 2 indicating the maximum correction are designated as variable values, the other intermediate values are automatically determined in response to them. be able to. The correction amount designating circuit 43 is for designating the correction amount, but since the subdivided designation is meaningless, it is preferable that it can be designated by means of a dip switch or the like. The correction pattern of the unit block is determined by specifying the correction pattern shape data and the correction amount. The correction pattern data is expanded by the gradation correction circuit 36 into each block in the main scanning direction to perform gradation correction.

As described above, according to the present embodiment, the relative position accuracy between the auxiliary electrode of the print head 2a and the recording needle block and the amount of block density unevenness that varies depending on the type of recording paper are freely adjusted. It is possible to set or change the correction amount, which makes it possible to always give the optimum correction.

By the way, in the pseudo multi-gradation conversion system,
As in the case of the error diffusion method or its modification method, the dot arrangement is random, and in the dot matrix method and the dither method, the dot positions are a periodic array with a predetermined pitch. The degree of influence of the block density unevenness differs from that of the case. In the former, the block density unevenness is very noticeable, and in the latter, it tends to be less noticeable. Therefore, the appropriate gradation correction amount also has different values. Therefore, in a device configured so that multiple pseudo-multi-tone conversion algorithms can be selected in the same device, if the optimum correction is set for one algorithm, the correction will be inappropriate for the other algorithm. The problem arises that

Therefore, in the present invention, the device is constructed as shown in FIG. This apparatus is provided with a first pseudo multi-gradation conversion circuit 45 and a second pseudo multi-gradation conversion circuit 46, and the pseudo multi-gradation conversion algorithms of the respective circuits are different. ing. The conversion pattern switching circuit 44 selects either one of the first and second pseudo multi-gradation conversion circuits 45 and 46. The gradation correction circuit 36 receives a command from the correction amount designating circuit 47 and the correction pattern shape circuit 48 to determine the correction condition. The correction amount designating circuit 47 and the correction pattern shape circuit 48 store a plurality of correction data. It holds and receives a signal from the conversion pattern switching circuit 44 and sends out one of them. Thus, the gradation correction circuit 36 connects the correction data in block units to perform correction calculation for the entire screen width. According to this structure, the correction condition is changed in association with the selection of the first and second pseudo multi-grayscale conversion circuits 45 and 46, and as a result, the problem of incorrect correction is prevented. To be done.

As described above, according to the present embodiment, the correction condition of the block density unevenness is automatically changed according to the selection of the pseudo multi-gradation conversion algorithm. Can be prevented.

[0048]

As described above in detail, according to the present invention, the correction characteristic is set according to the image density unevenness generated on the electrostatic recording paper, and the gradation of the multi-tone original image signal is corrected according to the correction characteristic. After that, the pseudo multi-gradation conversion is performed and supplied to the print head. Therefore, it is possible to prevent the occurrence of image density unevenness in the filled portion of the gradation image and always perform recording with good image quality. An electronic recording device can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a pseudo multi-gradation electrostatic recording device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a block density unevenness pattern for each density region and a correction curve for an intermediate density region, and a diagram for explaining a signal processing step of the apparatus.

FIG. 3 is a diagram showing a block density unevenness pattern for each density region and correction curves thereof, and a diagram showing a relationship between an arbitrary density region and its correction amount.

FIG. 4 is a block diagram showing a configuration of a pseudo multi-gradation electrostatic recording device according to an embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a block position on a matrix structure of a print head and a print image position, and a diagram showing an example of a correction curve per unit block.

FIG. 6 is a block diagram showing a configuration of a pseudo multi-gradation electrostatic recording device according to an embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a pseudo multi-gradation electrostatic recording device according to an embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration of a pseudo multi-gradation electrostatic recording device according to a conventional example, and a diagram showing a state of block density unevenness when all dots are solid printed.

FIG. 9 is a diagram showing a cross-sectional structure of a print head, and a diagram showing an arrangement of recording needles, connection, and arrangement of auxiliary electrodes.

[Explanation of symbols]

1 ... Electrostatic recording paper roll, 2 ... Multi-stylus electrostatic recording head, 2a ... Print head, 3, 10, 20, 3
0, 40 ... Image signal processing unit, 4 ... Developing head, 5 ... Guide roller, 6 ... Pressure contact roller, 7 ... Conveying roller, 8 ... Pinch roller, 9 ... Electrostatic recording paper, 11, 13 ... Recording needle, 12
a, 12b, 14 ... Auxiliary electrode, 31 ... Gradation original image signal receiving circuit, 32, 37 ... Pseudo multi-gradation conversion circuit, 33 ... Matrix distribution circuit, 34, 39 ... Print head driver circuit, 35, 36 ... Gradation Correction circuit, 38 ... Matrix conversion circuit, 40 ... Block correction data circuit, 41 ... Correction phase position command circuit, 42, 48 ... Correction pattern shape circuit, 4
3, 47 ... Correction amount designation circuit, 44 ... Conversion pattern switching circuit, 45 ... First pseudo multi-gradation conversion circuit, 46 ... Second pseudo multi-gradation conversion circuit.

Claims (1)

[Claims] 1. A matrix wiring in which a large number of recording needles arranged in a row in the main scanning direction are divided into blocks in units of a predetermined number, and recording needles belonging to non-adjacent blocks having the same positions are commonly connected. And a print head in which auxiliary electrodes are arranged corresponding to the blocks, and a multi-gradation original image signal is binary-converted to the print head by a predetermined pseudo multi-gradation conversion method. In the pseudo multi-gradation electrostatic recording apparatus, which supplies a signal to form a latent image on electrostatic recording paper and develops the latent image with toner to record a pseudo multi-gradation image, Pseudo-multi-gray scale electrostatic recording characterized in that a gradation correction means is provided for setting a correction characteristic in accordance with image density unevenness occurring on a recording paper and gradation-correcting the multi-gradation original image signal in accordance with the correction characteristic. apparatus.