JP2543264B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus whose image density can be easily adjusted.

[0002]

2. Description of the Related Art Conventionally, printers of various principles have been proposed as output terminals for personal computers, workstations, etc., but in recent years, laser beam printers using electrophotographic processes and laser technology (hereinafter referred to as LBP) have been proposed.
Is superior in terms of recording speed and printing quality, and is rapidly spreading. On the other hand, in the market, the demand for full color LBP is increasing, but full color LB
In the case of P, since color halftone image data is an output target, monochrome LBP generally needs to process binary data, whereas image processing based on halftone image data is generally required. There is a need to do.

Generally, in the case of an image output device to which an electrophotographic process such as LBP is applied, there is a problem in the stability of the electrophotographic process itself, and it is difficult to obtain a halftone image. Often used. Binarization by the dither method is often used to obtain a halftone image with a two-tone printer. The principle of the dither method will be described with reference to FIG.

The input image is divided into N × M blocks, and the pixel level in the block is compared with the N × M matrix thresholds for each pixel and binarized according to the magnitude relationship between the thresholds. By repeating this for each matrix size, a dither image is obtained. As the threshold matrix, there are a dot concentration type in which dots are concentrated and the gradation is smooth, and a dot dispersion type in which dots are dispersed and resolution is prioritized. FIG. 12 shows the circuit configuration of the binary dither method.
Comp is a comparison circuit, to which the input signal line In and the threshold matrix memory Mx are connected, and the output line Out.
Is provided. The pixels of the input image signal input through the input signal line In are sequentially moved, the rows and columns of the threshold matrix memory Mx are addressed correspondingly, and the respective threshold values are sequentially read to obtain the input image signal. Binarize by comparing large and small. The binarized recording image signal is output from the output line Out, sent to a printer engine (not shown), and printed.

[0005]

As described above, the LB
In an image output device such as a P or a thermal transfer printer in which the number of gradations of the process or the transfer principle itself is insufficient, the image data is binarized because the dither method is used in the halftone image part. There is a problem that it is difficult to adjust the density of image data.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an image forming apparatus in which image density adjustment is easy.

[0007]

In order to achieve the above object, the present invention is an image forming apparatus for performing gradation recording by changing the size of each dot based on input image data. Te, set comprised one block at a multiple of the number of pixels so, a block dividing means for dividing into a plurality of blocks by separating at a position for recording the image data, the priority in accordance with the position of the pixel in the block , A gradation processing unit that outputs a signal that makes a dot corresponding to a position of a pixel having a higher priority larger than a dot corresponding to a position of a pixel having a lower priority according to the density of image data; A recording unit that changes the dot size according to the output signal to perform recording, and a dot unit that corresponds to the position of the pixel with high priority in the block when lowering the image density
Adjust so that the dot size is recorded smaller.
That is obtained by a density adjusting means. If you want to increase the density of the image, move it to the position of the pixel with low priority in the block.
Only the corresponding dots will be recorded with a large dot size.
A density adjusting means for adjusting the above is provided.

[0008]

According to the present invention, with the above configuration, the dot corresponding to the position of the pixel having the high priority is made larger than the dot corresponding to the position of the pixel having the low priority, thereby giving priority to the image data of the pixel having the low priority. In addition to recording with dots corresponding to the position of this high priority pixel included in the pixels with high priority, when reducing the image density, only the dot corresponding to the position of the high priority pixel in the block It
To reduce the concentration . In addition, when increasing the image density, the position of the low priority pixel in the block
Only the dots corresponding to
To raise .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a block diagram of an image forming apparatus according to an embodiment. 22 is a digital data output device,
An image signal from an image scanner, a video camera, or the like (not shown) is input, A / D conversion, predetermined image processing are performed, and image data is temporarily stored in a memory. Alternatively, it is an interface or the like which receives an image signal directly from the communication means.

When the print engine 21 is activated, the digital data output device 22 starts transferring the digital image data and the image discrimination signal to the image processing section 23. The data to be subjected to the image processing is 8 bits for each color of red, green, blue (hereinafter referred to as RGB), that is, a total of 24 bits. Image processing unit 2
The RGB data input to 3 is brightness data, and the density conversion unit 24 converts the brightness data into density data, that is, cyan, magenta, and yellow (hereinafter referred to as CMY) which are the three primary colors of printing. Generally, this conversion is a conversion of the characteristics as shown in FIG. 2, and a conversion table 25 in which conversion table data is written is provided on a readable / writable memory (hereinafter referred to as RAM), for example, an input data value is appropriately offset and accessed. This can be easily achieved. The normal density conversion unit 24 performs monochromatic density / total density / contrast / base color control (density and color adjustment) of the input image.

RGB (luminance) data is CM after density conversion.
Each signal line 26, 27, 2 converted into Y (density) data
It is output to No.8, and CMY data is used to
The CR29 performs UCR processing (undercolor removal) and black plate generation.
The UCR process is performed by reducing the data at a constant rate with respect to the common amount of CMY data. Basically, this reduction amount is generated as a black plate. Originally, the purpose of the UCR processing and black plate generation is to replace the common amount of CMY with black in each pixel to save the color material (toner). However, today, UCR and black plate generation are rarely performed purely to save toner, and for the purpose of preventing gradation deterioration in high density areas, ensuring contrast, and ensuring gray balance in high density areas, for example, It is possible to positively change the amount of UCR processing and black plates and output a higher quality image. After the UCR processing and black plate generation by the above processing, C data, M data, Y data and Bk (black) data are generated on the respective data lines 30, 31, 32. After that, the Bk data other than the achromatic component is input to the color correction unit 34. In the color correction unit 34, processing such as masking is performed on the color components (CMY). The purpose of masking is to correct the effect of unwanted absorption bands of each color material. For example, C (cyan) color material is C
It has an unnecessary absorption band in wavelength regions other than. Specifically, for example, it has a Y (yellow) color component. Also M (magenta)
Similarly, Y is included. Therefore, when recording Y, it is necessary to reduce the Y component contained in C and M according to the density at which C and M should be recorded. The method is usually C
3 × 3 matrix calculation for MY digital signal,
Alternatively, the calculation result is written in a storage device such as a read-only memory (hereinafter referred to as ROM), and this is accessed and added / subtracted for each color to obtain a predetermined result. Conventional 3 ×
Although 3 linear masking (1st order masking) was the mainstream, the effect of 1st order masking is insufficient, and recently nonlinear masking of 2nd order or higher, or color correction itself is regarded as a mapping performed in a black box, and CMY is used. A number of new color correction methods for obtaining mapping functions outside of space have also been proposed.
Data on the input data C line 30 by the color correction unit 34,
The data on the M line 31 and the data on the Y line 32 are the data on the C ′ line 35, the data on the M ′ line 36,
It is converted into data on the Y'line 37. On the other hand, Bk line 3
The data above 3 are achromatic data and therefore do not participate in color correction.

C ′ color-corrected by the color correction unit 24
As for the data on the line 35, the data on the M ′ line 36, the data on the Y ′ line 37 (colored data), and the data on the Bk line 33 (achromatic data), only the data of one color is selected by the data selector 38. , And is input to the gradation processing unit 39 to perform gradation processing.

The contents of the gradation processing unit 39 will be described in detail with reference to FIGS. FIG. 3 shows a circuit block of the gradation processing unit 29. The gradation conversion input image signal line 41 is inputted to the image gradation conversion table 53, and the gradation conversion output image signal is inputted to the image gradation conversion table 53. The line 42 is connected. Since it is necessary to change the gradation characteristic depending on the recording color, the gradation conversion corresponding to each color can be performed by inputting the recording color signal on the signal line 43 to each gradation conversion table 53.

In a color recorded image, a screen angle method is used to avoid moire between recorded colors. The image is divided into 4 × 4 blocks, and each block is divided into two pixels, a pixel to be grown first and a pixel to be grown later. As shown in FIGS. 4 (a) to 4 (d), the method of dividing the two is different for each of the recording colors Bk, C, M, and Y.
A screen angle of Bk45 ° C63.6 ° M26.4 ° Y0 ° is formed to avoid moire due to interference between recording colors. In the gradation processing unit shown in FIG. 3, reference numeral 50 is a horizontal synchronizing signal generating circuit A, which generates a signal indicating the time interval of one pixel of the image signal. The horizontal quaternary counter A52 counts the output of the horizontal synchronizing signal generating circuit A50 in quaternary and outputs a 2-bit count value. Reference numeral 56 is a vertical synchronizing signal generating circuit A, which generates a vertical synchronizing signal at a predetermined time interval required for gradation processing. The vertical quaternary counter A58 counts the vertical synchronizing signal in quaternary and outputs a 2-bit count value. The position of the currently input image data in the 4 × 4 block is determined based on these two count signals.

The data values of the pixels that grow first and the pixels that grow later are converted into level signals for actually driving the laser, for example, pulse width data by the conversion table for each address. The conversion method is, for example, ROM or RA.
The simplest and most reliable method is to write data in M and call the position information of the block and the level of the input image signal as an address. FIG. 5 shows conversion table characteristics of data of a pixel which grows first and a pixel which grows later.
(A), It shows in FIG.5 (b).

The image data converted into the actual laser drive data for each address in the block as described above is
It is stored in an image memory as a gradation conversion output image signal.

In the present embodiment, at the stage of processing a halftone image, the spatial position of the image data is separated into a pixel to be grown first and a pixel to be grown later, and the data is concentrated on the pixel to be grown first. Since it is forcibly performed, the effect of generating a strong electric field in a small area of the electrostatic latent image on the photoconductor is very large, which contributes to the improvement of gradation.

Further, in the present embodiment, the size of the block is described as 4 pixels in the main scanning direction and 4 pixels in the sub scanning direction in the process of performing the halftone image processing, but the size is not limited to this, and it may be any size. However, it does not matter how many pixels in the block are preferentially subjected to dot growth. Further, in the embodiment, the screen angle is formed by changing the pixel to be grown earlier in the block to suppress the occurrence of moire, but the moire can be avoided even if the size of the block is made different for each recording color. it can.

The recorded image stored in the image memory is read from the image memory as a density adjustment input image signal on the line 61 (see FIG. 6) in synchronization with the operation of the print engine 21, and the present invention is performed by the density adjusting unit 40 according to the present invention. The density adjustment processing related to is performed.

The contents of the density adjusting section 40 are shown in FIGS. 6 and 7 (a).
~ It demonstrates in detail using FIG.7 (d). FIG. 6 shows a circuit block of the density adjusting section 40. The density adjustment input image signal on the line 61 is input to the density adjustment conversion table 73. The line 62 is connected to the density adjustment conversion table 73 and outputs the density adjustment output image signal. Since it is necessary to change the gradation characteristic depending on the recording color, the density adjustment according to each color can be performed by inputting the recording color signal on the line 63. In the gradation conversion unit, the image is divided into 4 × 4 blocks by using a screen angle method in order to avoid moire between recording colors, and pixels to be grown first in each block and later Although it is divided into two pixels to be grown, even in the gradation processing of FIG. 6, the horizontal quaternary counter B72 and the vertical quaternary counter B78 are used to determine at which position within the 4 × 4 block the image data currently input. It is determined whether or not there is, and the pixels to be grown first and the pixels to be grown later are distinguished for each recording color.

The data values of the pixels that grow first and the pixels that grow later are converted in the level of the image signal by the conversion table 73 for each address so that density adjustment can be easily and effectively performed. The conversion method is, for example, ROM or RA.
The simplest and most reliable method is to write data in M and call the position information of the block and the level of the input image signal as an address.

In the present invention, the density adjustment processing is performed as shown in FIG.
As shown in FIGS. 7A to 7D, when the density is lowered, the recording signal level is lowered only for the pixels to be grown first, and when the density is increased, the recording signal level is raised only to the pixels to be grown later. It is a method. Even if the level of the recording signal is changed in both pixels, it is not possible to adjust the density at all, but if the density is lowered, lowering both pixels will result in no further recording signal if there is no dot in the pixel to be grown later. However, the density adjustment amount for each block differs from that in the case where there are pixels to be grown later. According to the present invention, it is possible to perform uniform density adjustment by shaving a pixel having a dot to reduce the density and increasing a pixel having no dot to increase the density.

The recorded image data whose density has been adjusted for each address in the block as described above is sent to the print engine 21 and the density of the recorded image for the purpose of the present invention can be adjusted.

Next, the laser beam printer is shown in FIG.
It will be described in detail with reference to FIG.

A laser beam printer for forming a color image to which an electrophotographic process technique is applied selectively irradiates a light beam corresponding to each color on a photosensitive member having a photosensitive layer to form an image, thereby forming a plurality of predetermined color components. A method of forming a color image on one transfer material by developing a plurality of electrostatic latent images respectively corresponding to specific components in the above with respective predetermined toners and superposing the toner images of the single color. It is adopted.

FIG. 8 is a side sectional view of the laser beam printer,
FIG. 9 is a perspective view for explaining the operation of the photosensitive member reference detection, and FIG.
FIG. 6 is a perspective view illustrating an operation of detecting an intermediate transfer member reference.

In FIG. 8, 101 is a closed loop resin having a seam 101a on the outer peripheral surface of a belt base material,
It is a photoreceptor in which a photosensitive layer such as selenium (Se) or an organic photoconductor (OPC) is applied in a thin film form. This photoconductor 1
01 is supported by the two photoconductor transport rollers 102 and 103 so as to form a vertical plane, and is rotated in the direction of arrow A along the photoconductor transport rollers 102 and 103 by a drive motor (not shown). On the peripheral surface of the belt-shaped photoconductor 101, the charger 10 is arranged in the order of the photoconductor rotation direction indicated by an arrow A.
4, exposure optical system 105, developing devices 106B, 106C, 106M and 106Y for each color of black (B), cyan (C), magenta (M), and yellow (Y), intermediate transfer body unit 107, and photoconductor cleaning device 108. A static eliminator 109 and a photoconductor reference detection sensor 110 are provided.

The charger 104 comprises a charging wire 111 made of a tungsten wire or the like, a shield plate 112 made of a metal plate, and a grid plate 113. Charging line 1
By applying a high voltage to 11, the charging line 111 causes corona discharge, and the photoconductor 10 passes through the grid plate 113.
1 is uniformly charged. Reference numeral 114 is an exposure light beam of image data emitted from the exposure optical system 105. In the laser beam printer, the exposure light beam 114 is obtained by applying an image signal, which is obtained by modulating an image signal from a gradation converter by light intensity modulation or pulse width modulation by a laser drive circuit (not shown), to a semiconductor laser (not shown). To form a plurality of electrostatic latent images corresponding to specific components among a plurality of predetermined color components on the photoconductor 101.

As shown in FIG. 9, the photoconductor reference detection sensor 110 detects the position of the seam 101a of the photoconductor 101, and it is predetermined at one end of the photoconductor 101 with respect to the seam 101a of the photoconductor 101. The photoconductor reference mark 101b such as a slit arranged at the determined position is detected.
In FIG. 8, each color developing device stores a toner corresponding to each color. The color of the toner is selected according to each color, and the developing device selected by rotating the separation / contact cams 115B, 115C, 115M, and 115Y whose both ends are pivotally supported by the main body of the machine in response to the color selection signal. For example 106B
Is brought into contact with the photoconductor 101. The remaining undeveloped developing units 106C, 106M, 106
Y is separated from the photoconductor 101. The intermediate transfer body unit 107 is a seamless loop belt-shaped intermediate transfer body 116 made of a conductive resin or the like, and two intermediate transfer body transport rollers 117 and 118 supporting the intermediate transfer body 116.
To transfer the toner image on the photosensitive member 101 to the intermediate transfer member 116, the intermediate transfer member 116 is sandwiched between the photosensitive member 101 and the photosensitive member 101.
And an intermediate transfer roller 119 arranged so as to oppose thereto. Here, the surface perimeter L1 of the photoconductor 101 is designed to be equal to the surface perimeter L2 of the intermediate transfer member 116, but it is set so that the relationship of L1 ≦ L2 is always established within the range of the variation. .

10, reference numeral 120 denotes an intermediate transfer member reference detection sensor for detecting the reference position of the intermediate transfer member 116, which is an intermediate transfer member reference mark 116a such as a slit arranged at one end of the intermediate transfer member 116. To detect the reference position. In FIG. 9, reference numeral 121 denotes a photoconductor clutch mechanism, which controls rotation of the photoconductor by connecting / disconnecting power from a drive source (not shown).
3 are provided on the drive shaft. In FIG. 8, reference numeral 122 denotes an intermediate transfer member cleaning device for scraping off the residual toner on the intermediate transfer member 116, which is separated from the intermediate transfer member 116 while a composite image is formed on the intermediate transfer member 116. It comes into contact only when it is used for cleaning. 123
Is a transfer body cassette that contains the transfer material 124.
The transfer materials 124 are sent out from the transfer material cassette 123 one by one to a paper transport path 126 by a half-moon shaped paper feed roller 125. 127 is the transfer material 124 and the intermediate transfer member 11.
6 is a registration roller for temporarily stopping and waiting the transfer material 124 in order to match the positions of the composite images formed on the sheet 6, and is in pressure contact with the driven roller 128. Reference numeral 129 is a transfer roller for transferring the composite image formed on the intermediate transfer member 116 to the transfer material 124.
Only when the image is transferred to No. 4, the intermediate transfer member 116 is contacted and rotated.
Reference numeral 130 denotes a fixing device including a heat roller 131 having a heat source inside and a pressure roller 132, and the combined image transferred on the transfer material 124 is pressed and heated as the heat roller 131 and the pressure roller 132 are nipped and rotated. By transfer material 124
And fix it to form a color image.

The operation of the electrophotographic apparatus configured as described above will be described below.

The photosensitive member 101 and the intermediate transfer member 116 are each driven by a driving source (not shown), and are controlled so that their peripheral speeds are the same constant speed. Further, an image forming area of the intermediate transfer member 116 is set in advance by an intermediate transfer member reference detection sensor 120 for detecting an intermediate transfer member reference mark 116a for determining a reference position, and a seam 101a of the photosensitive member 101 is set in this region. Are adjusted so that they do not overlap at the intermediate transfer roller 119, and are driven in synchronization.

In this state, first, a high voltage is applied to the charging wire 111 in the charger 104 connected to the high voltage power source to cause corona discharge, and the surface of the photoconductor 101 is uniformly -700 v to-.
Charge to about 800v. Next, move the photoconductor 101 to the arrow A
On the surface of the photoconductor 101 which is rotated in a predetermined direction and is uniformly charged, for example, a predetermined black (B) among a plurality of color components is formed.
When the exposure beam 114 of the laser beam corresponding to is irradiated, the electric charge disappears in the irradiated portion on the photoconductor 101, and an electrostatic latent image is formed. At this time, the electrostatic latent image is formed on the photosensitive member 101 at a position within the image area on the intermediate transfer member 116, which is set in advance by a signal from the intermediate transfer reference detection sensor 120 that detects the reference position of the intermediate transfer member 116. Seam 1
It is formed avoiding 01a. On the other hand, the developing device 106B storing the black toner contributing to the development is pushed in the direction of arrow B by the rotation of the separation / contact cam 115B by the color selection signal, and comes into contact with the photoconductor 101. With this contact, the photoconductor 1
Toner adheres to the electrostatic latent image portion formed on 01 to form a toner image, and development is completed. Developing device 1 after development
06B is moved from the contact position with the photoconductor 101 to the separation position by rotating the separation cam 115B by 180 degrees. The toner image formed on the photoreceptor 101 by the developing device 106B is transferred to the intermediate transfer body 116 by applying a high voltage to the intermediate transfer roller 119 arranged in contact with the photoreceptor 101 for each color. From the photoconductor 101 to the intermediate transfer body 1
The residual toner that has not been transferred to 16 is removed by the photoconductor cleaning device 108, and the charge on the photoconductor 101 from which the residual toner has been scraped off is removed by the static eliminator 109.

Next, for example, when a color of cyan (C) is selected, the separation cam 115C is rotated, and this time the developing device 106C is pushed toward the photoconductor 101 and brought into contact with the photoconductor 101, so that the cyan (C) color is changed. Start development. In the case of a copying machine or printer using four colors, the above developing operation is sequentially repeated four times to form toner images of four colors B, C, M and Y on the intermediate transfer member 116 to form a composite image. In the composite image thus formed, the sheet transfer roller 129, which has been separated so far, comes into contact with the intermediate transfer member 116, and a high pressure is applied to the sheet transfer roller 129, and pressure is applied from the transfer material cassette 123 to the sheet conveyance path 126. Transfer material 124 sent along
Are collectively transferred to. Subsequently, the transfer material 124 on which the toner image is transferred is sent to the fixing device 130, where the heat roller 1
It is fixed by the heat of 31 and the nip pressure of the pressure roller 132 and is output as a color image. The residual toner on the intermediate transfer body 116, which is not completely transferred onto the transfer material 124 by the sheet transfer roller 129, is removed by the intermediate transfer body cleaning device 122. The intermediate transfer member cleaning device 122 keeps the intermediate transfer member 1 until one composite image is obtained.
At a position apart from 16, a composite image is obtained, and the composite image is transferred to the transfer material 124 by the sheet transfer roller 129 and then comes into contact with the residual material to remove the residual toner.

By the above operation, the recording of one image is completed, and the color recorded image with the density adjusted is obtained.

The printer is not limited to the electrophotographic system using the laser beam of this embodiment, and may be a thermal transfer system, an inkjet system, or the like, and may be a light emitting diode array which is one of the electrophotographic systems. It may be the one used or the one using a liquid crystal shutter. Further, in the present embodiment, the color image is superposed on the intermediate transfer member, but it may be superposed on the photosensitive member or on the transfer paper.

[0038]

As described above, according to the present invention, by making the dot corresponding to the position of the pixel having the high priority larger than the dot corresponding to the position of the pixel having the low priority, the image of the pixel having the low priority is obtained. Since data is included in the pixels with high priority and recording is performed with dots corresponding to the positions of the pixels with high priority, when forming an image with low density, all dots should be of the same size according to the density. A desired density can be stably obtained for the image forming apparatus for recording, and gradation can be improved. Furthermore, when lowering the image density, it corresponds to the position of the pixel with high priority in the block
Reduce the density by reducing the size of the dots
Since that, especially if the concentration is low, the position of the lower priority pixel
As compared with the case of reducing the density by reducing the size of the dot corresponding to, the range in which the dot can be reduced is wide, and thus the density can be surely reduced. Also, position of pixels with low priority in the block when increasing the density of the image
The dot size corresponding to the
The density is increased by increasing the dot size corresponding to the position of the pixel with high priority, especially when the density is high.
Compared with the case of increasing, it can be increased reliably concentration for a wide range it is possible to increase the dot.

[Brief description of drawings]

FIG. 1 is a block diagram of an image forming apparatus of the present invention.

FIG. 2 is a graph of the density conversion characteristics.

FIG. 3 is a circuit block diagram of the gradation processing unit.

FIG. 4 is a layout diagram of pixels to be grown first for each recording color in the same halftone image portion.

FIG. 5 is a gradation characteristic diagram of the same pixel.

FIG. 6 is a circuit block diagram of the density adjusting unit.

7A is a graph of the same density adjustment table characteristics, FIG. 7B is a graph of the same density adjustment table characteristics, FIG. 7C is a graph of the same density adjustment table characteristics, and FIG. 7D is a graph of the same density adjustment table characteristics.

FIG. 8 is a side sectional view of the laser beam printer.

FIG. 9 is a perspective view illustrating an operation of the photosensitive member reference detection.

FIG. 10 is a perspective view for explaining the operation of the intermediate transfer member reference detection.

FIG. 11 is a perspective view showing the principle of a conventional binary dither method.

FIG. 12 is a block diagram of a circuit that performs the process of the binary dither method.

[Explanation of symbols]

 23 image processing unit 24 density conversion unit 25 density conversion table 29 UCR / black plate generation unit 34 color correction unit 39 gradation processing unit 40 density adjustment unit

Claims (2)

(57) [Claims] 1. An image forming apparatus for performing gradation recording by changing the size of each dot based on input image data, wherein one block is composed of a plurality of pixels. a block dividing means for dividing into a plurality of blocks by separating at a position for recording the image data, determines the priority according to the position of the pixel in the previous Symbol block, high priority according to the density of the image data A gradation processing unit that outputs a signal that makes a dot corresponding to a pixel position larger than a dot corresponding to a pixel position having a low priority, and a dot size is changed according to an output signal from the gradation processing unit. The recording means for recording and the pixel of high priority in the block when lowering the image density
Only the dots corresponding to the position are recorded with a small dot size
An image forming apparatus characterized in that a concentration adjusting means for adjusting to be. 2. An image forming apparatus for performing gradation recording by changing the size of each dot based on input image data, wherein one block is composed of a plurality of pixels. a block dividing means for dividing into a plurality of blocks by separating at a position for recording the image data, determines the priority according to the position of the pixel in the previous Symbol block, high priority according to the density of the image data A gradation processing unit that outputs a signal that makes a dot corresponding to a pixel position larger than a dot corresponding to a pixel position having a low priority, and a dot size is changed according to an output signal from the gradation processing unit. The recording means for recording and the pixel of low priority in the block when increasing the image density
Larger dot size is recorded only for the dots corresponding to the position
An image forming apparatus characterized in that a concentration adjusting means for adjusting to be.