JP2000138829A - Image processing unit, image processing method and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing unit that can express medium gradation by the error spread method, without degrading resolution and gradation number of an image. SOLUTION: This image processing unit 21, that conducts processing to reproduce medium gradation, is provided with an error spread processing section 217 that applies error spread processing to received image data, a mean density calculation section 219 that calculates the mean density of a very small area consisting of a target pixel and its surrounding pixels required for the error spread processing by the error spread processing section 217, and a pulse width modulation section 218 that modulates a pulse width with respect to the target pixel, where the error spread processing is conducted depending on the density calculated by the mean density calculation section 219.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and an image processing method for processing and reproducing a density gradation of an image to be formed by an error diffusion method when an image is formed by a printer, for example. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art There is an error diffusion method as a processing method for reproducing the gradation of an image to be formed when image data read by an image reading device such as an image scanner is formed by a printer. The error diffusion method is one of pseudo halftone reproduction methods for achieving both resolution and gradation of an input image, and realizes gradation of an input image by density gradation.

However, in an actual printer, when an image is formed by performing image processing by an error diffusion method, a dot pattern that is randomly turned on / off generated by the error diffusion cannot be accurately reproduced. There's a problem. This is, for example, in the case of 8-bit image data,
The gradation is expressed as 256 steps from 0 to 255. When this is processed by the error diffusion method and an image is formed (printed) on a sheet, white (off) is generated due to the printing characteristics of the printer. When the area ratio of black (ON) is less than 100%, the density of the printed image is saturated and 25%.
The problem is that six gradations cannot be obtained.

Here, in a printer such as a laser printer in which the dot diameter can be changed for each pixel by modulating the pulse width, a gradation expression using binary data is performed by this error diffusion method. Here is an example. FIG.
FIG. 7 is a diagram showing density reproduction characteristics when uniform image data from 0 to 255 is processed by the error diffusion method and printed, and FIG. 7 is a diagram in which image data with uniform three gradations is actually printed. FIG. 7A is a diagram showing an example (FIG. 7A shows a case where the gradation of the input image data is 16, and similarly, FIG. 7B shows 64 and FIG. 7C shows 128). As can be seen from each figure, where the gradation of the input image data is low, the image density reproduced on the paper is lower, while where the gradation is high, the image density is reproduced higher. . In particular, FIG.
, It can be seen that the white dots in the black dots are difficult to reproduce.

[0005] The cause of such a phenomenon is that pulse width modulation is performed for each pixel. Therefore, where the gradation is low, the size of one dot is small.
Due to the blurring of the dots, the reproduced image density is low. Conversely, where the gradation is high, the size of one dot is large, and the dots formed on the paper are also blurred. Because of the tendency of enlargement due to image collapse or the like, the reproduced image becomes darker, and as shown in FIG. The concentration saturates.

Conventionally, as a method for improving such a phenomenon, before performing error diffusion processing, image data is gamma-converted in accordance with the above-described printer characteristics to thereby obtain a printed image density. Does not use parts that are not reproduced because they are saturated.

More specifically, as shown in FIG. 8, conversion is performed using a gamma conversion table. As can be seen from FIG.
Since the portion up to the point is used, the density to be reproduced is eventually degraded to the number of gradations shown at the k point.

Further, since the image data is gamma-converted in a portion having a medium density or higher, the density is equivalently reduced, so that the number of lighted pixels in the thin line portion is not gamma-converted. Decrease compared to the case. This affects the formation of an image whose contour is sharp, particularly for characters.

FIG. 9 shows an example of a character printed by performing error diffusion processing without performing gamma conversion.
FIG. 8 shows an example of characters printed by performing gamma conversion using the gamma conversion table shown in FIG. 8 and then performing error diffusion processing. As can be seen from these figures, if density adjustment is performed by gamma conversion before error diffusion processing, the number of illuminated pixels decreases, and in particular, the resolution decreases in a thin line portion,
The reproducibility is deteriorated. This is because the gamma conversion itself is performed based on the density reproduction characteristics when the density flat portion is subjected to error diffusion processing and output by a printer, so that the density is not flat in a thin line portion such as a character outline. Therefore, the contour portion (thin line) is blurred as shown in FIG.

On the other hand, as a method for preventing blurring of dots at the time of low gradation, Japanese Patent Laid-Open No. 5-7295 discloses a method in which pulse width modulation is performed for every two pixels to make the dots extremely small at the time of low gradation. A technique for preventing such a situation has been disclosed.

However, according to the method disclosed in this publication alone,
It cannot be improved that the image density is saturated in a portion where the gradation value is high.

[0012]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image processing apparatus and method capable of performing a process for expressing gradation by an error diffusion method without reducing the resolution and the number of gradations of an image. And an image forming apparatus using the image processing apparatus.

It is another object of the present invention to provide an image processing apparatus using an error diffusion method in which the resolution in a thin line portion is improved.

[0014]

The object of the present invention is achieved by the following means.

(1) In an image processing apparatus for performing processing for reproducing an intermediate gradation, error diffusion processing means for performing error diffusion processing on input image data, and error diffusion processing performed by the error diffusion processing means. Density calculating means for calculating the density of the minute area composed of the target pixel and its surrounding pixels, and the target pixel on which error diffusion processing has been performed by the error diffusion processing means according to the density calculated by the density calculating means. And a pulse width modulating means for modulating a pulse width of the image processing apparatus.

(2) In an image processing apparatus for performing processing for reproducing an intermediate gradation, error diffusion processing means for performing error diffusion processing on input image data, and error diffusion processing is performed by the error diffusion processing means. A black pixel number calculating means for calculating the number of black pixels in a minute area composed of the pixel of interest and its surrounding pixels; and an error diffusion processing means according to the black pixel number calculated by the black pixel number calculating means. An image processing apparatus, comprising: pulse width modulation means for performing pulse width modulation on a pixel of interest on which diffusion processing has been performed.

(3) The image processing apparatus further includes character area determining means for determining an area corresponding to a character from the image data, and the pulse width modulation means includes a character area determining means for determining the character area by the character area determining means. The duty ratio of the pulse width modulation in the region determined to be 100% is set to 100%.

(4) In an image processing method for reproducing an intermediate gradation, a step of performing an error diffusion process on input image data, and a minute pixel including a target pixel and its peripheral pixels when performing the error diffusion process. Calculating the density of the region;
Performing a pulse width modulation on a pixel of interest on which the error diffusion processing has been performed in accordance with the calculated density.

(5) In the image forming apparatus, error diffusion processing means for performing error diffusion processing on the input image data, and a minute pixel including a pixel of interest and its surrounding pixels when error diffusion processing is performed by the error diffusion processing means. Density calculating means for calculating the density of the region, and pulse width modulating means for modulating the pulse width of the pixel of interest subjected to the error diffusion processing by the error diffusion processing means in accordance with the density calculated by the density calculating means An image forming apparatus comprising:

(6) In the image forming apparatus, error diffusion processing means for performing error diffusion processing on the input image data, and a small area comprising a target pixel subjected to error diffusion processing by the error diffusion processing means and its peripheral pixels And a pulse width for the target pixel on which the error diffusion processing is performed by the error diffusion processing unit according to the number of black pixels calculated by the black pixel number calculation unit. An image forming apparatus comprising: a pulse width modulation unit that performs the modulation of the above.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

Embodiment 1 FIG. 1 is a block diagram for explaining a schematic configuration of an image forming system to which the present invention is applied.

In this system, an image scanner (hereinafter, simply referred to as a scanner) 10 for reading an image drawn on a sheet, image data read by the scanner 10 are input, and image processing described later is performed to perform image processing on the sheet. And a scanner 20 for forming the
And a personal computer 30 for controlling the printer 20.

Here, the scanner 10 is capable of reading a color image, and has a CCD color image sensor, as is well known, and is capable of reading an original (sheet-like original or book) on which an image is drawn. The scanner unit 11 reads a color image for each of R, G, and B colors by scanning, and the image processing unit 12 outputs the read image data to the printer 20 as 8-bit digital image data for each color.

On the other hand, as will be described later in detail, the printer 20 is an image processing section 21 which performs various processes required for image formation on image data input from the scanner 10.
And a printer engine 22 for forming an image on a sheet in accordance with the image-processed data, and a controller 23 for receiving a control signal from a personal computer 30 and controlling the printer 20 in accordance with the control signal. Here, the printer engine 22 forms an image by a well-known electrophotographic method, emits a semiconductor laser according to the width of a pulse sent from the image processing unit 21, and forms an electrostatic latent image on a photosensitive drum. An image is formed, the latent image is developed with toner, and the developed toner image is formed on a sheet (paper or O
An image is formed by fixing to an HP film or the like.

The personal computer 30 transfers the image data read by the scanner 10 to the printer 20 and controls the timing when the image data is output (printed) by the printer 20. In this case, It does not directly relate to the processing of image data. The personal computer 30
In addition to the above, it is also possible to perform processing such as storing and processing image data read by the scanner 20, and output image data drawn by the personal computer 30 to the printer 20 for printing. It can also be done.

Next, a portion related to image processing in the image forming system configured as described above will be described focusing on the configuration and functions of the image processing section 21 provided in the printer 20.

FIG. 2 is a block diagram for explaining the configuration of the image processing section 21.

The image processing section 21 compresses image data for each of R (red), G (green), and B (blue) colors input from the scanner 10 and stores the compressed data in the memory 211. Compression / expansion unit 210 for expanding the expanded data, logarithmic conversion unit 212 for converting the expanded image data based on the luminance signal of each of R, G, and B to image data based on the density signal, and image data of each of the R, G, and B colors A color conversion unit 213 that converts the color of the image data into C (cyan), M (magenta), and Y (yellow) data; a UCR / BP unit 214 that extracts black from the C, M, and Y image data;
An image correction unit 215 for performing TF correction and smoothing filter processing; and a resolution conversion unit 21 for complementing image data and adjusting to the output resolution when the input image resolution from the scanner 10 and the output image resolution by the printer are different.
6 and one pixel of image data (8-bit data) output from the resolution conversion unit 216, and compares the density of the pixel with a predetermined threshold to obtain binary data (1 bit data). And an error diffusion processing unit 217 for diffusing an error between the actual density of the binarized pixel and the density of a pixel captured thereafter, and a density calculation unit 2 described later.
And a pulse width modulation unit 218 that modulates the width of a pulse to be output in accordance with the density data from the image processing unit 19. In the first embodiment, image data input to the error diffusion processing unit 217, that is, error diffusion The pixel of interest to be processed;
Average density calculation unit 2 for calculating the average density of the peripheral pixels
19, and a character area determination unit 220 that determines a character area from image data.

The compression / expansion unit 210 and the logarithmic conversion unit 21
2. The color conversion unit 213, the UCR / BP unit 214, the image correction unit 215, the resolution conversion unit 216, and the error diffusion processing unit 217 are the same as those in an image processing apparatus provided in a well-known electrophotographic color printer. Since these units are the same as those of the respective units, detailed descriptions of these functions and operations are omitted. The error diffusion process is also normally performed. Therefore, here, this error diffusion processing will be briefly described. First, the pixel data input to the error diffusion processing unit 217 is determined based on a predetermined threshold value, and is converted into binary data (1 bit data) of black (ON) or white (OFF). Become. At this time, a difference occurs between the actual density and the target pixel that has become black or white, and the difference is diffused to pixels subsequent to the target pixel according to a predetermined relational expression. Thereafter, the diffused density is added to the original density of the pixel of interest to be subjected to the next error diffusion processing, and the binarization and diffusion processing is similarly performed as the next pixel of interest. In the error diffusion process, the density of the target pixel is diffused and stored in peripheral pixels by sequentially performing such a process.

Hereinafter, the functions and operations of the average density calculating section 219 and the character area determining section 220 and the modulation of the pulse width by the pulse width modulating section 218 will be described.

The average density calculating section 219 is provided by the resolution converting section 2
The image data output from the pixel 16 is fetched, and the fetched image data of one pixel is regarded as a pixel of interest (a pixel on which error diffusion processing is performed). Calculate the value. Here, an average of the densities of a region of 5 × 10 pixels composed of pixels around the target pixel is set. Therefore, the average density calculation unit 219 has a memory (not shown), which stores the density data of each pixel for five lines including the pixel of interest, and stores the density data centered on the pixel of interest among the five pixels. An area corresponding to × 10 pixels is extracted, and the average density is obtained.

Note that the method of obtaining the minute area is not limited to such a range, and the size of the minute area and the relationship between the target pixel and its surrounding pixels may be appropriately adjusted.

The average density of the minute area including the pixel of interest calculated as described above is used to form dots corresponding to the pixel of interest (pixels subjected to error diffusion processing and output as binary data). And is output to the pulse width modulation section 218 as a 6-bit control signal for determining the pulse width. For the output of this control signal, a look-up table (LUT) 230 is prepared as shown in FIG. 3, in which a density gradation (8-bit data) and a pulse width control signal (6-bit data) are associated. The value of the control signal to be output is determined based on the LUT 230. LUT2 used at this time
As shown in FIG. 3, reference numeral 30 has a modulation curve that makes the pulse width narrower as the density increases.

Therefore, the binary data of the pixel of interest output from the error diffusion processing unit 217 is
At 8, the pulse width modulated by the modulation curve shown in FIG. 3 is output to the printer engine 22. At this time, the binary data of the pixel of interest output from the error diffusion processing unit 217 and the control signal output from the average density calculation unit 219 for modulating the pulse width are synchronized with each other. Like that.

By the above processing, as shown in FIG.
The density characteristic of the image reproduced by the printer 20 (solid line in FIG. 4) is reproduced up to a point beyond the point k which cannot be reproduced by saturation in the characteristic of the conventional printer (dotted line in FIG. 4). This is because dot collapse does not occur even at high density, the density saturation point moves to higher density, the gradation expression range is widened, and white isolated points are well reproduced. On the other hand, in a place where the density is low, black isolated points can be reproduced well without causing blurring of dots.

Next, the functional operation of the character area determination section 220 will be described.

The character area judging section 220 includes the compression / decompression section 21
R, G, and B data output from 0 are fetched, and a character area is determined for each area.

The result of the determination is input to the image correction unit 215 and the average density calculation unit 220. The image correction unit 215 executes different filtering processing depending on the obtained character area determination result, that is, whether or not the area is a character area.

On the other hand, in the average density calculating section 220,
In the area determined to be a character area from the input determination result, a control signal for modulating the pulse width so that the duty ratio is 100% is provided regardless of the average density value in the minute area described above. Output. That is, 63 (for 6-bit data) is output as the pulse width value in the LUT shown in FIG.

As a result, in the character portion, a larger dot area is printed in the image after the error diffusion processing, and it is possible to prevent the resolution of the thin line from being reduced by the error diffusion processing. The drawn character has a sharp outline.

Here, the character area determination section 220 compares, for example, the density (or luminance) of a pixel at the center in a minute area with the average density of surrounding pixels, and the difference is equal to or greater than a reference value. Whether or not the central pixel is a character area, a photograph area, or a halftone area is determined depending on whether or not the pixel is a center area. Such a method is disclosed in, for example, Japanese Patent Application Laid-Open No.
As disclosed in, for example, Japanese Patent Application Laid-Open No. 247436/1990, there are various methods for determining whether or not a character area is present, and the present invention may employ any method. Here, detailed description is omitted.

By executing the above-described processing for each of the colors C, M, Y, and K, a color image with good gradation can be reproduced without lowering the resolution.

Embodiment 2 Next, another embodiment to which the present invention is applied will be described.

In the second embodiment, the number of black pixels is calculated from the target pixel subjected to the error diffusion processing and its surrounding pixels, and the pulse width is determined according to the obtained number of black pixels. FIG. 5 is a block diagram illustrating a configuration related to image processing in the image processing system according to the second embodiment. The overall configuration of the image processing system is the same as that shown in FIG. 1 in the first embodiment.
In the block diagram shown in FIG. 5 as well, components having the same functions as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The image processing unit 51 according to the second embodiment shown in FIG. 5 is provided in the printer 20 similarly to the first embodiment, and includes a compression / expansion unit 210, a logarithmic conversion unit 212, a color Conversion unit 213, UCR / BP unit 21
4. The image correction unit 215, the resolution conversion unit 216, the error diffusion processing unit 217, the pulse width modulation unit 218, and the character area determination unit 220 perform the same functions and operations as in the first embodiment.

In the second embodiment, the image data binarized by the error diffusion processing unit 217 is input to the pulse width modulation unit 218 and the black pixel calculation unit 511
Is also entered. The black pixel calculation unit 511 calculates the number of black pixels in a pixel (target pixel) on which error diffusion has been performed and its surrounding pixels. Here, the term “black pixel” refers to a pixel that is turned on (printed) as binarized pixel data after error diffusion, and is referred to as a black color ( K) does not mean a pixel to be displayed.

Then, the pulse width of the target pixel is determined in accordance with the calculated number of black pixels, and the control signal is sent to the pulse width modulator 218.
A pulse width corresponding to the number of surrounding black pixels is output to the printer engine 22.

Here, the number of black images is calculated, for example, from a small area of about 5 × 10 surrounding pixels around the pixel of interest. For this reason, the black pixel calculation unit 511 has a memory (not shown) for storing pixel data for five lines including the target pixel. Of the image data stored in this memory, The number of data that is turned on is counted from among the 5 × 10 pixels around the target pixel and around the target pixel.

In order to determine the pulse width from the calculated number of black pixels, the relationship between the number of black pixels and the corresponding pulse width is stored in advance as an LUT 512 in the same manner as in the first embodiment. Done by reference. At this time, the relationship between the number of black pixels and the pulse width is such that the larger the number of black pixels, the narrower the pulse width for the target pixel, while the smaller the number of black pixels, the wider the pulse width. Thereby, when the number of black pixels is large, that is, even when the density of the original image is high, the dots to be printed are small, so that pixel collapse and the like do not occur,
It is possible to print without saturating the dark density. On the other hand, when the number of black pixels is small, that is, when the density of the original image is low, black isolated points can be reproduced well without blurring of dots.

Also, in the second embodiment, the first embodiment
Similarly, in the character portion, the pulse width of the pixel in the character portion is set to 100% based on the determination result from the character region determination portion 220. For this reason, in the black pixel number calculation unit 511, the character area determination unit 220
When the result of the determination is a character portion, a control signal for modulating the pulse width to be 100% is output. As a result, in the character portion, as in the first embodiment, a larger dot area is printed after the error diffusion process, and a reduction in resolution in the character portion caused by the error diffusion process can be prevented. The reproduced character has a sharp outline.

By executing the above-described processes for each of the colors C, M, Y, and K, a color image with good gradation can be reproduced without lowering the resolution.

In each of the embodiments described above, the image forming system is configured by using the separately configured scanner, printer, and personal computer that controls these components. The present invention has such a configuration. However, the present invention is not limited to this. For example, as in a full-color digital copying machine, a scanner, a printer engine, and a control unit that controls these components may be integrally configured. Further, as in each embodiment, even in an image forming system in which a scanner, a printer, and a personal computer for controlling the scanner and the printer are separately configured, one of the scanner and the printer controls the timing of reading and outputting an image. It is also possible to omit the personal computer by providing a control unit for performing the operation. Of course, the present invention can be applied not only to a color image but also to a monochrome image. Furthermore, the present invention can be appropriately modified by those skilled in the art within the scope of the technical idea of the present invention.

[0054]

According to the present invention described above, the following effects can be obtained for each claim.

According to the image processing apparatus of the first aspect of the present invention, the dot diameter at the time of printing the target pixel is determined based on the density of the peripheral pixel area including the target pixel for the error diffusion processing. Since the pulse width to be controlled is modulated, the pulse width can be adjusted according to the density around the target pixel.For example, when the density is high, the pulse width is reduced, and when the density is low, By increasing the pulse width, it is possible to reduce the density saturation due to the collapse of dots in the high density portion of the reproduced image, while preventing the blurring of the dots when the density is low, and lowering the resolution. Without this, it is possible to maintain a wide gradation.

According to the image processing apparatus of the present invention, for the target pixel subjected to the error diffusion processing, the number of black pixels is calculated from the peripheral pixel region including the target pixel, and the number of black pixels is calculated. Since the pulse width for controlling the dot diameter when printing the target pixel is modulated in accordance with, for example, after error diffusion, when the number of black pixels is large, that is, when the density of the original image is high, the pulse By narrowing the width and increasing the pulse width when the number of black pixels is small, that is, when the original density is low, density saturation due to dot collapse etc. is reduced in the high density part of the reproduced image. On the other hand, when the density is low, it is possible to prevent the fading of the dots, and without lowering the resolution.
It is possible to maintain a wide gradation.

According to the image processing apparatus of the present invention, since the character area is determined and the duty ratio of the pulse width modulation is set to 100% in the character part, a thin line such as an outline in the character part is obtained. Can be improved.

According to the image processing method of the fourth aspect of the present invention, for a target pixel to be subjected to error diffusion processing, the dot diameter at the time of printing the target pixel is determined based on the density of the surrounding pixels including the target pixel. Since the pulse width to be controlled is modulated, the pulse width can be adjusted according to the density around the target pixel.For example, when the density is high, the pulse width is reduced, and when the density is low, By increasing the pulse width, it is possible to reduce the density saturation due to the collapse of dots in the high density portion of the reproduced image, while preventing the blurring of the dots when the density is low, and lowering the resolution. Without this, it is possible to maintain a wide gradation.

According to the image forming apparatus of the fifth aspect of the present invention, for a target pixel to be subjected to error diffusion processing, the dot diameter at the time of printing the target pixel is determined based on the density of the peripheral pixel area including the target pixel. Since the pulse width to be controlled is modulated, the pulse width can be adjusted according to the density around the target pixel.For example, when the density is high, the pulse width is reduced, and when the density is low, By increasing the pulse width, it is possible to reduce density saturation due to crushing of dots in a portion where the density of an image to be formed is high, and to prevent blurring of dots when the density is low, thereby lowering resolution. Without this, it is possible to maintain a wide gradation.

According to the image forming apparatus of the present invention, for the target pixel subjected to the error diffusion processing, the number of black pixels is calculated from the peripheral pixel area including the target pixel, and the number of black pixels is calculated. Since the pulse width for controlling the dot diameter when printing the target pixel is modulated in accordance with, for example, after error diffusion, when the number of black pixels is large, that is, when the density of the original image is high, the pulse By narrowing the width and increasing the pulse width when the number of black pixels is small, that is, when the original density is low, the density saturation due to dot collapse and the like is reduced in the high density part of the formed image. On the other hand, when the density is low, it is possible to prevent the fading of the dots, and without lowering the resolution.
It is possible to maintain a wide gradation.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image forming system to which the present invention has been applied.

FIG. 2 is a block diagram illustrating an image processing unit according to the first embodiment.

FIG. 3 is a diagram illustrating a conversion curve of an LUT according to the first embodiment.

FIG. 4 is a drawing for explaining a print output density with respect to a value of input data in the first embodiment.

FIG. 5 is a block diagram illustrating an image processing unit according to a second embodiment.

FIG. 6 is a diagram showing a print output density with respect to a conventional input data value.

FIG. 7 is a diagram showing a conventional print output result;
FIG. 6A shows a case where the gradation value of the input image data is 16;
Is also 64, FIG. 6C is also 128,
Shown respectively.

FIG. 8 is a drawing showing an example of a gamma conversion curve.

FIG. 9 is a diagram for explaining the reproducibility of characters when gamma conversion is not performed.

FIG. 10 is a diagram for explaining the reproducibility of characters when gamma conversion is performed.

[Explanation of symbols]

 Reference Signs List 10: scanner, 20: printer, 21, 51: image processing unit, 217: error diffusion processing unit, 218: pulse width modulation unit, 219: average density calculation unit, 220: character area determination unit, 230, 512: LUT ( Look-up table), 511: Black pixel number calculation unit.

Continued on the front page F term (reference) 2C262 AA05 AA24 AA26 AB07 AC19 BB08 BB47 DA09 EA04 EA07 5B057 BA25 CA07 CB07 CB08 CC02 CE13 5C077 MP05 MP06 MP08 NN11 NN17 PP27 PP28 PP46 PP61 PP68 PQ05 PQ18 TT03

Claims (6)

[Claims] 1. An image processing apparatus for performing a process for reproducing an intermediate gradation, comprising: an error diffusion processing unit for performing an error diffusion process on input image data; Density calculating means for calculating the density of a minute area consisting of the target pixel and its surrounding pixels; and, based on the density calculated by the density calculating means, for the target pixel on which error diffusion processing has been performed by the error diffusion processing means. An image processing apparatus comprising: pulse width modulation means for performing pulse width modulation. 2. An image processing apparatus for performing a process for reproducing a halftone, comprising: an error diffusion processing unit for performing an error diffusion process on input image data; Black pixel number calculating means for calculating the number of black pixels in a minute area composed of pixels and peripheral pixels, and error diffusion by the error diffusion processing means according to the number of black pixels calculated by the black pixel number calculating means. An image processing apparatus comprising: a pulse width modulation unit configured to perform pulse width modulation on a pixel of interest on which processing has been performed. 3. The image processing apparatus according to claim 1, further comprising: a character area determination unit configured to determine an area corresponding to a character from the image data; 2. The duty ratio of pulse width modulation in an area determined to be present is set to 100%.
Or the image processing device according to 2. 4. An image processing method for reproducing an intermediate gradation, comprising: a step of performing an error diffusion process on input image data; and a minute area including a pixel of interest and a peripheral pixel when performing the error diffusion process. An image processing method, comprising: calculating a density of the target pixel; and performing a pulse width modulation on the pixel of interest on which the error diffusion processing has been performed according to the calculated density. 5. An image forming apparatus, comprising: an error diffusion processing unit for performing an error diffusion process on input image data; and a small area including a pixel of interest and its peripheral pixels when the error diffusion processing unit performs an error diffusion process. Density calculating means for calculating the density of, and, according to the density calculated by the density calculating means, a pulse width modulation means for modulating the pulse width of the pixel of interest subjected to error diffusion processing by the error diffusion processing means, An image forming apparatus comprising: 6. An image forming apparatus, comprising: an error diffusion processing unit for performing an error diffusion process on input image data; and a small area including a target pixel subjected to the error diffusion process by the error diffusion processing unit and its peripheral pixels. Black pixel number calculating means for calculating the number of black pixels; and, according to the number of black pixels calculated by the black pixel number calculating means, the pulse width of the target pixel on which error diffusion processing has been performed by the error diffusion processing means. An image forming apparatus comprising: pulse width modulation means for performing modulation.