JP2003060905A - Image processing method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing method and apparatus that can prevent pixel missing in an image of a character part, to prevent the quality of a character image from deteriorating. SOLUTION: A black character discrimination section 110 discriminates a character part in a received image, discriminates character edge parts and the inside of characters, and outputs a discrimination result signal 121. A filter 107 increases the density level of image signals in the inside of the character and uses a screen with the number of 266 lines to apply PWM modulation to the image signals in the inside of the character to form the image. A screen with 400 lines in number applies PWM modulation to the character edges to form the image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and apparatus for improving image reproducibility by performing image area separation on an image.

[0002]

2. Description of the Related Art Conventionally, in a digital copying machine equipped with a laser beam printer, a character portion of an original image is formed at a high resolution by giving priority to resolution, and in an image portion such as a photograph, stability is emphasized and dots are formed. It was concentrated and formed with low resolution. However, with resolution priority and emphasis on stability,
Since the settings are contradictory, the image area of the original image is separated into the character portion and the image portion, and proper image formation control is performed for each, so that a high-quality image is recorded in both the character portion and the image portion. The method of doing was taken. There are various methods for such image area separation. For example, there is a method of detecting the edge portion of a character, detecting the character portion, and classifying the image with other images.

Further, conventionally, the space between the edges of a character is recognized as the inside of the character, and the character edge portion forms an image at a high resolution in order to make the character look clear, and a low resolution in the character for smooth reproduction. , The image processing is changed according to the image area. For example,
In the image forming apparatus having the highest resolution of 400 dpi, the character edge portion is image-formed at 400 dpi, the image portion and the inside of the character are formed at 200 dpi, and the image portion and the inside of the character are stable by gathering dots with a low line number. The image is being output. Further, in the character edge portion, the resolution is increased with a high number of lines to improve the reproduction of characters. Further, in order to emphasize the edges of the characters and reproduce clear characters, the edges are emphasized by a filter process to reproduce the characters.

Next, the line number generation processing conventionally used in a digital laser copying machine or the like will be described. Figure 11
(A) and (B) are pulse width modulation (hereinafter referred to as PW) for expressing gradation in a conventional digital laser copying machine.
It is a figure explaining M). Here, the triangular wave 1101 is compared with the signal level of the inverted image data 1100, and the signal (PWM signal) 11 is turned on only when the signal level of the inverted image data 1100 is higher than the level of the triangular wave 1101.
02 is output to drive the laser for lighting. That is, when the reverse image data level is high, the width of the laser light is short and the density is low, and when the reverse image data level is low, the width of the laser light is long and the density is high. 11A shows the signal generation timing in the case of 400 lines, and FIG. 11B schematically shows the signal generation timing in the case of 200 lines. It is shown in. When the normal image data is displayed in 8 bits of 0 to 255, the inverted image data is obtained by subtracting the image data from 255 and input to the PWM circuit as the inverted image data.

Here, for example, as shown in FIG. 8, when outputting the portion of the character 301 determined to be the character edge 1200 and the character inside 1201 other than the character, FIG.
As shown in (B), the character edge portion 1200 is PWMed with 400 lines, and the character inside 1201 is PWMed with 200 lines. The PWM signals 1203 and 120 generated in this way
A laser lighting signal is generated from 4. In this case, depending on the phase of the PWM signal, 12 in FIGS.
The case of 03 or 1204 appears.

The method described above is a method of sequentially forming CMYK images on one drum, and in order to improve the gradation reproduction of the gradation part, the image part which is not judged as a character is 200 lines. The image was being formed. Further, in the ideal case where PWM of 400 lines and 200 lines is not delayed at all, the black character processing described above is performed. Therefore, as shown in FIGS. 12 (A) and 12 (B), the character end is 4
There was no particular problem with either the 00 line or the 200 line inside the character.

[0007]

However, with the increase in speed of printers, printers having four drums (hereinafter referred to as four drums) are used to form CMYK images on different drums. It has become. In this four-drag, since images of four respective colors are formed by using different drums, registration misalignment cannot be avoided, and it is general that the images are screened and output during image formation. In addition, in order to prevent screen interference for each color when forming a screen, the black screen ruling is changed from the screen ruling of another color. For example, C and M are 2
In contrast to the 00 line, in the case of K (black), the 266 line is used.

As described above, it has been found that when the number of K lines is 266, moire due to interference with the screens of other colors can be prevented, but the compatibility of reproducing black characters deteriorates.

This will be described with reference to FIGS. 13A and 13B by taking a screen generation method of 400 lines and 266 lines as an example.

As shown in FIG. 13A, in the case of 400 lines, one triangular wave is formed within one pixel. On the other hand, in the case of the 266 line, as shown in FIG.
In the case of a line, 1.5 pixels form one triangular wave. As described above, in the case of 266 lines, one triangular wave is formed by 1.5 pixels, so there is no problem with data that is constant image data, but in the case shown in FIG.
That is, if the end of the character is 400 lines and the inside of the character is 266 lines, the image data 1402 and the triangular waves 1400 and 14
It has been found that, depending on the phase of 01, the image data of one pixel is not reproduced at all, and the inside of the character may appear white. In FIG. 14A, 1400 is 400
A triangular wave in the case of a line is shown, and 1401 is a triangular wave in the case of a 266 line. In the case of FIG. 14B, 2
Since the phase of the triangular wave 1401 of the 66th line is different from that in the case of FIG. 14A, the pixel is not blank.

In addition, CMs are sequentially placed on one conventional drum.
Even with the method of forming YK images, 400 lines and 200 lines
In the case where there is a shift in the PWM waveform of the line as shown in FIGS. 15A and 15B, for example, in the case of FIG. I found out that it turned white.

As described above, since the data that should be printed in only one pixel is not printed, white spaces may occur between the edges of characters, resulting in deterioration of character quality.

The present invention has been made in view of the above-mentioned conventional example, and an object of the present invention is to provide an image processing method and apparatus which prevent pixel omission in an image of a character portion to prevent deterioration of character image quality.

[0014]

In order to achieve the above object, the image processing apparatus of the present invention has the following configuration.
That is, an image area determination unit that determines the character portion in the input image and determines the character edge portion and the inside of the character portion, and the character edge portion and the character inside determined by the image area determination unit Resolution setting means for setting the resolution for forming the character portion, and adjusting means for adjusting the level of the image signal in the image according to the character edge portion and the inside of the character determined by the image area determination means. And the density level of the image determined to be inside the character is increased by using the adjusting means.

In order to achieve the above object, the image processing method of the present invention comprises the following steps. That is, an image area determination step of determining the character portion in the input image and determining the character edge portion and the inside of the character portion, and the character edge portion and the inside of the character determined in the image area determination step are performed. A resolution setting step of setting a resolution for forming the character portion, and an adjusting step of adjusting the level of the image signal in the image according to the character edge portion and the inside of the character determined in the image area determination step. And the density level of the image determined to be inside the character is increased by using the adjustment process.

[0016]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[First Embodiment] FIG. 1 is a block diagram showing the functional arrangement of an image processing apparatus according to the first embodiment of the present invention.

In FIG. 1, a scanner 101 reads an original image to generate RGB signals (R0, G0, B0),
Each is quantized into 8 bits and output. The input masking unit 102 performs masking processing according to the reading characteristics of the scanner 101, and outputs R1, G1, and B, respectively.
Converted to 1 signal and output. These R1, G1, and B1 signals are input to the background removal unit 103, the background components are removed, and they are converted into R2, G2, and B2 signals. These R2, G
The 2, B2 signals are input to the logarithmic conversion unit 104 and logarithmically converted, and the density signals Cyan (cyan), Magenta (magenta), and Yellow (yellow) signals (C0, M0, Y).
0). These CMY signals (Y0, M0, C
0) is further input to the black extraction unit 105, undercolor removal is performed, a black signal K (Black) is generated, and C1, M1, Y
1, K1 signals are output.

Next, these C1, M1, Y1, and K1 signals are sent to the output masking section 106, and the printer section 1
A masking process according to the print characteristics of 09 is performed. Here, based on a determination result signal 121 supplied from a black character determination unit 110 described later, processing such as outputting a black character portion in black (K) single color is performed, and C2,
The M2, Y2 and K2 signals are output. These C2, M
Based on the determination result signal 121 from the black character determination unit 110, the 2, Y2, K2 signals are filtered by the filter unit 107 so that the image portion is output smoothly and the character portion is output clearly by edge emphasis. And the result is C
The 3, M3, Y3 and K3 signals are output to the γ conversion unit 108. The γ conversion unit 108 performs gamma conversion set by the user and gamma conversion according to the gradation characteristics of the printer unit 109, and the gamma-converted C4, M4, Y4, and K are converted.
The four signals are output to the printer unit 109.

The black character determination unit 110 receives the R1, G1, B1 signals from the input masking unit 102, determines the black character portion in the original image, and outputs the determination result as signal 1
At 21, the output masking unit 106, the filter 107, and the C
It is output to PU11. The CPU 111 controls the flow of image processing in this image processing apparatus, and this control processing is executed according to the program stored in the memory 112.

Next, the black character determination unit 110 will be described with reference to FIG.

FIG. 2 shows a black character determination unit 1 according to this embodiment.
It is a block diagram which shows the structure of 10.

In the input masking section 102, the scanner 10
The R1, G1, and B1 signals converted by the masking process according to the reading characteristic in No. 1 are converted into the binarizing unit 201.
Is input to the color determination unit 205. In the binarization unit 201,
In the case where the respective values of the R1, G1 and B1 signals have a certain threshold value, for example, 8 bits, the value is binarized to white (0) when it is "100" or more and to black (1) when it is less than that.

FIG. 3 is a diagram showing an example of an original image, and FIG. 4 is a diagram showing an example of binarization of the original image.

The color determination unit 205 calculates the difference between the R1, G1 and B1 signals, for example, (GR) and (GB), and in the case of black, both of these differences are small. When the difference is small, it is determined as black. Then, the judgment result is fed back to the binarization unit 201. As a result, the binarization unit 201 determines the character portion that is black based on the binarized data obtained earlier and the color determination result in the color determination unit 205, and the rising determination unit 202 sends the binarization processing result ( 4) is output.

The rising determination unit 202 detects the rising of a character, for example, the pixel position where the character changes from white to black, and in the above example, for example, detects the beginning portion of the character as shown in FIG.

Further, the trailing edge judging section 203 detects the trailing edge of the character, for example, the pixel position where black changes to white,
For example, in the above-mentioned example, as shown in FIG. 6, the pixel at the position where the character ends is detected. Finally, the internal character determination unit 204
Includes a rising portion (FIG. 5) at the beginning of a character in the main scanning direction determined by the rising determination portion 202 and a falling portion (FIG. 6) that is the end portion of the character determined by the falling determination portion 203. , The pixel inside the character (FIG. 7) is detected by excluding it from the binarization result of FIG. 4 (FIG. 4). Thus, finally, from the black character determination unit 110, a determination result signal (121 in FIG. 1) divided into a character edge portion (a character rising portion and a character falling portion) and a character internal signal. ) Is generated. This determination result signal 12
1 is “0” in the image portion other than the character, and the character edge 30
2 is "1", and inside the character 303 is "2". The filter 10 based on the determination result signal 121
7. The number of lines in the printer unit 109 is as follows, for example. Judgment result signal 121 = 0: The image part other than the character, the number of lines of the printer 109 is 266 line judgment result signal 12
1 = 1: character edge part, the number of lines of the printer 109 is 400
Line determination result signal 121 = 2: Inside the character, the printer 10
The number of lines of 9 is changed like 266 lines.

Specifically, in order to clearly reproduce a character, the filter 107 intensifies edge emphasis in the character edge portion, and the image portion other than the character is smoothed by the filter 107 to suppress moire. Further, as in the conventional case, the inside of the character is smoothed similarly to the image portion other than the character, and the final data is as shown in FIG.

If this state is left as it is, a defect of missing pixels occurs as shown in FIG. 14A. Therefore, in the present embodiment, as shown in FIG. The DC component of the filter 107 was increased so that the output was darker than the actual concentration. By doing so, it is possible to reliably reproduce the pixel data that has disappeared due to the phase. For example, in the image formation by the 400/266 line of the portion cut out at 301 in FIG. 8, the pixel omission occurred conventionally as shown in FIG. 14A, but in the present embodiment, it is shown in FIG. As shown in, the level of the image data is lowered. As a result, conventionally
In the present embodiment, the pixel omission occurs as shown in FIG. 10B, but the pixel omission is prevented in the present embodiment as shown in FIG. 10C. As a result, white spots in pixels are reduced, and good characters can be reproduced.

Also, 400/200 lines are 400 lines and 20 lines.
In the image formation when the triangular wave of the 0 line is shifted, the image is conventionally as shown in FIG. 15A, but in the present embodiment, it is as shown in FIG. Good characters can be reproduced. 16 and 17, the image data level indicated by the dotted line indicates the level of conventional image data, and the image data level indicated by the solid line corresponds to the image data level of this embodiment. At this time, an image is formed darker than the actual document, but this is not a problem even if the inside of the character is darkened because the edge of the character is originally edge-enhanced.

FIG. 21 is a flow chart for explaining the processing in the image processing apparatus according to the first embodiment of the present invention.

First, in step S1, image data is input,
In step S2, the character part in the input image,
It is determined to be an image part such as a graphic or photograph other than that. Next, in step S3, in the area determined to be the character portion, the edge portion of the character portion and the inside of the character are determined,
A determination result signal 121 indicating the determination result is output. Next, in step S4, it is determined whether it is a character edge or the inside of a character.
Set to a line. On the other hand, if it is inside the character, step S6.
Go to and set to 266 lines, then go to step S7,
Raise (make darker) the signal level of the image signal inside the character. Then, in step S8, PWM modulation is performed to form an image.

As described above, according to the first embodiment, it is possible to prevent omission of pixels inside a character by increasing the density level inside the character.

[Second Embodiment] FIG. 18 is a block diagram showing the arrangement of an image processing apparatus according to the second embodiment of the present invention.
Portions common to the configuration of the first embodiment (FIG. 1) described above are denoted by the same symbols, and description thereof is omitted. In the above-described first embodiment, the value of the image data inside the character is increased by the filter 107, but in the image processing apparatus according to the second embodiment, the γ conversion unit 108 inputs the black character determination signal 121, The same effect can be obtained by the following method based on the value of the determination signal 121.

Black character determination signal 121 = 0: γ = 1.0 in non-character image portion, black character determination signal 121 = 1: at character edge portion, γ = 1.0 black character determination signal 121 = 2: inside character, If γ = 1.2, the data inside the character and the data of the character edge are
Similar to the first embodiment, the image formation result by the PWM is as shown in FIG. 10C, and it is possible to prevent the pixel data inside the character from being lost.

FIG. 22 is a flow chart for explaining the processing in the image processing apparatus according to the second embodiment of the present invention.

First, in step S11, image data is input, and in step S12, the character portion and the image portion in the input image are determined. Next, in step S13,
In the area determined to be the character portion, the edge portion of the character portion and the inside of the character are determined, and the determination result signal 121 indicating the determination result is output. Next, the process proceeds to step S14, it is determined whether or not it is a character portion, and if it is an image portion other than the character portion, the process proceeds to step S15 and the 266 line and γ coefficient are set to "1.0"
Set to.

In step S14, if it is a character portion, the process proceeds to step S16 to determine whether it is a character edge or the inside of a character. Set to 0 ". On the other hand, if it is inside the character, the process proceeds to step S18 and the line 266 is set, and the γ coefficient is set to “1.2”. After executing any one of steps S15, S17, and S18 in this way, the process proceeds to step S19, and γ conversion is executed based on the γ coefficient set in the previous step. Then, the process proceeds to step S20,
An image is formed by performing PWM modulation.

[Third Embodiment] In the first and second embodiments described above, the amount of increase in pixel data inside a character is constant, but the user can change the increase amount according to the level of pixel omission. By making it possible, the optimum value may be set according to the printer unit 109.
For example, a pattern as shown in FIG. 19 is output instead of the reading signal of the scanner 101, and the user can visually determine the optimum data amount of the inside of the character by reproducing the reproduced amount of the thin portion in the middle through actual processing. . In particular,
An operation unit including key switches 2000 and 2001 as shown in FIG. 20 is provided, and the numerical value is increased by instructing the key switch 200, and the numerical value is decreased by instructing the key switch 2001 while changing the numerical value. It can be visually set as appropriate. Explaining the case of the third embodiment, the set value of γ is, for example, as follows.

Character internal data increase amount 0: γ = 1.0 Character internal data increase amount 1: γ = 1.1 Character internal data increase amount 2: γ = 1.2 Character internal data increase amount 3: γ = 1.3 Character internal data increase amount 4: γ = 1.4 The above setting is merely an example, and the present invention is not limited to this.

FIG. 23 is a block diagram for explaining generation of a semiconductor laser driving PWM signal in the printer unit 109 according to the present embodiment.

In the figure, 2300 is a comparator, 2
Reference numeral 301 denotes a triangular wave signal generator that generates a triangular wave signal having a frequency for 400 lines. 2302 is a triangular wave signal generator for generating a triangular wave signal having a frequency for 266 lines. 23
A selector 04 selects the triangular wave signal from either the triangular wave signal generator 2301 or 2302 in accordance with the switching signal 2305 for selecting either the 400 line or the 266 line and outputs it to the comparator 2300. The comparator 2300 includes the γ conversion unit 108 described above.
Image data is input, the signal level of this image data is compared with the signal levels of the triangular wave signals selected by the selector 2304, and a PWM signal which is the comparison result is generated. This PWM signal is sent to, for example, a semiconductor laser (not shown) to form an image.

Even when the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), a device including one device (for example, a copying machine, a facsimile device, etc.) ) May be applied.

Another object of the present invention is to supply a storage medium (or recording medium) recording a program code of software for implementing the functions of the above-described embodiments to a system or apparatus, and to supply a computer (or computer) of the system or apparatus. It is also achieved by the CPU or MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiment are realized, but also an operating system (OS) running on the computer is executed based on the instruction of the program code. This also includes a case where a part or all of the actual processing is performed and the processing realizes the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written in the memory provided in the function expansion card inserted in the computer or the function expansion unit connected to the computer, based on the instruction of the program code. It also includes a case where the CPU provided in the function expansion card or the function expansion unit performs a part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

As described above, according to the present embodiment, it is possible to prevent the deterioration of character quality by changing the image processing of the portion determined to be inside the character in the image. For this purpose, for example, the gain of the filter inside the character is made higher than before, and the data level of the 266 line part is raised to prevent one pixel omission, thereby improving the character quality.

As another embodiment, the tone inside the character is increased, the data level of the 266 line portion is increased to prevent one pixel omission, and the character quality is improved.

Further, the data level can be set by the user so that it can be set to the optimum value for the user, and the best image can be supplied to the user.

[0049]

As described above, according to the present invention, there is an effect that it is possible to prevent pixel omission in the image of the character portion and prevent deterioration of the quality of the character image.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a black character determination unit according to the present embodiment.

FIG. 3 is a diagram showing an example of an input original image.

4 is a diagram showing an example of binarization of the original image data of FIG.

5 is a diagram showing rising data of the binarized data of FIG.

FIG. 6 is a diagram showing falling data of the binarized data of FIG.

7 is a diagram showing character internal data of the binarized data of FIG.

FIG. 8 is a graph of 2 in FIG. 4 in the black character determination unit of the present embodiment.
It is a figure explaining the determination result with respect to value-ized data.

FIG. 9 is a diagram showing an example of a final image formed by the image processing apparatus according to the present embodiment.

FIG. 10 is a diagram showing an example of an image output result by the image processing apparatus according to the present embodiment.

FIG. 11 is a diagram illustrating conventional image formation by switching between 400 lines and 200 lines.

FIG. 12 is a diagram illustrating conventional image formation by switching between 400 lines and 200 lines.

FIG. 13 is a diagram illustrating conventional image formation by switching between 400 lines and 266 lines.

FIG. 14 is a diagram illustrating conventional image formation by switching between 400 lines and 266 lines.

FIG. 15 is a diagram illustrating conventional image formation by switching between 400 lines and 266 lines.

FIG. 16 is a diagram illustrating image formation by switching 400 lines and 266 lines according to the present embodiment.

FIG. 17 is a diagram illustrating image formation by switching between 400 lines and 266 lines according to the present embodiment.

FIG. 18 is a block diagram showing a configuration of an image processing device according to a second embodiment of the present invention.

FIG. 19 is a diagram illustrating an input image pattern according to the third embodiment of the present invention.

FIG. 20 is a diagram illustrating an operation on the operation unit according to the third embodiment of the present invention.

FIG. 21 is a flowchart showing image processing in the image processing apparatus according to the first embodiment of the present invention.

FIG. 22 is a flowchart showing image processing in the image processing apparatus according to the second embodiment of the present invention.

FIG. 23 is a diagram for explaining generation of a PWM signal in the image processing device according to the embodiment of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/387 101 B41J 3/00 A 5L096 1/407 MF term (reference) 2C262 AB13 AC17 AC19 BB01 BB15 BB29 BB38 BB41 BB42 BB44 DA02 DA03 DA09 DA13 DA16 EA04 EA07 EA16 GA01 2C362 AA54 AA63 CB02 CB04 CB07 CB23 CB24 5C074 AA02 BB03 DD07 DD14 DD16 DD24 DD28 FF03 HH02 5C076 AA21 BA06 BB22 5C077 LL04 LL19 MP02 MP06 MP08 NN17 PP15 PP20 PP27 PP28 PP32 PP33 PP38 PQ05 PQ08 PQ12 PQ20 SS02 TT03 5L096 AA02 AA06 BA07 CA14 DA01 EA43 FA06 FA44 GA02 GA40 MA03

Claims (14)

[Claims] 1. A character portion in an input image is discriminated,
An image area determination unit that determines the character edge portion and the inside of the character portion, and a resolution for forming the character portion according to the character edge portion and the inside of the character that are determined by the image area determination unit are set. Resolution setting means, and adjusting means for adjusting the level of the image signal in the image according to the character edge portion and the character inside determined by the image area determining means, and the inside of the character is determined. An image processing apparatus, wherein the density level of an image is increased by using the adjusting means. 2. The image processing according to claim 1, wherein the resolution setting means sets the resolution by setting the screen ruling for the character edge portion higher than the screen ruling for the inside of the character. apparatus. 3. The image processing apparatus according to claim 1, wherein the adjusting unit includes a filter, and changes the image signal level for the inside of the character so as to increase the density level. 4. The image according to claim 1, wherein the adjusting means includes a γ converter, and a γ conversion coefficient for the inside of the character is made larger than a γ conversion coefficient for an image portion other than the character. Processing equipment. 5. The image processing apparatus according to claim 1, further comprising setting means for setting the γ conversion coefficient in the γ converter. 6. A PWM for generating a PWM signal based on the image signal with a resolution set by the resolution means.
The image processing apparatus according to claim 1, further comprising: a unit and an image forming unit that forms an image using the PWM signal generated by the PWM unit. 7. A character portion in an input image is discriminated,
An image area determination step of determining a character edge portion and a character inside of the character portion, and a resolution for forming the character portion according to the character edge portion and the character inside determined in the image area determination step are set. A resolution setting step, and an adjusting step of adjusting the level of the image signal in the image according to the character edge portion and the inside of the character determined in the image area determining step, and the inside of the character is determined. An image processing method, wherein the density level of an image is increased by using the adjustment process. 8. The image processing according to claim 7, wherein in the resolution setting step, the screen ruling for the character edge portion is set to be higher than the screen ruling for the inside of the character to set the resolution. Method. 9. The image processing method according to claim 7, wherein the adjusting step includes a filtering process, and the image signal level for the inside of the character is changed so as to increase the density level. 10. The image processing method according to claim 7, wherein the adjusting step includes a γ conversion, and a γ conversion coefficient for the inside of the character is made larger than a γ conversion coefficient for an image portion other than the image portion. . 11. The image processing method according to claim 7, further comprising a setting step of setting the γ conversion coefficient. 12. A PWM step of generating a PWM signal based on the image signal at the resolution set in the resolution step, and an image forming step of forming an image using the PWM signal generated in the PWM step, The image processing method according to any one of claims 7 to 11, further comprising: 13. A computer-readable storage medium in which a program for executing the image processing method according to claim 7 is stored. 14. A program for executing the image processing method according to any one of claims 7 to 12.