JP6634873B2 - Image forming apparatus and image optimization method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image optimizing method.

  In an image forming apparatus such as a printer or a copying machine, by repeatedly performing image formation, a line width of a character or the like to be formed changes, and image quality may be deteriorated. In order to accurately and stably reproduce characters, it is general to adjust parameters used for image processing of original image data or settings of an image forming engine to optimize an image to be formed.

For example, with respect to a change in line width, a test pattern in which fine lines are arranged is formed on a sheet, the read image data obtained by reading the sheet surface is analyzed, and the line width of the thin line is evaluated. The original image data is thinned so as to have a line width (for example, see Patent Document 1).
Further, an adjustment value of the line width in the thinning process is changed according to a difference or a ratio between a measured value of the line width formed on the paper and a target value (for example, see Patent Document 2). .

JP-A-2015-4702 JP 2015-35643A

  By forming a test pattern, it is possible to determine whether or not character deterioration has occurred.Conventionally, a test pattern is formed periodically, or a test pattern is formed when character deterioration is suspected. We had determined that we needed to perform the optimization. However, if the character has already deteriorated before the test pattern is formed, the image with the deteriorated character continues to be formed until the image is optimized.

  In addition, a certain resolution is required to detect a change in the line width of a character from the read image data on the paper surface. It is difficult.

  An object of the present invention is to easily detect deterioration of a character and execute image optimization at a timing when the deterioration occurs.

According to the invention described in claim 1,
An image forming unit that forms an image on paper based on the original image data;
An image reading unit that reads a sheet surface on which an image is formed by the image forming unit and generates read image data;
A control unit that analyzes the read image data and executes optimization of an image formed by the image forming unit;
A storage unit for storing a character pixel ratio and font information of a reference of each character,
The control unit includes:
The position of a character area is determined for each character based on the attribute information and font information of the character added to the original image data, and one or more rectangles are formed so as to include one or more character areas and their background areas. Extracting a region from the read image data, calculating a character pixel ratio formed in each rectangular region,
The character pixel rate of each rectangular area calculated in the read image data of the 1st to nth pages of paper on which the image is formed by the image forming unit immediately after executing the image optimization is defined as the character pixel rate of the reference. Stored in the storage unit together with font information of a character area included in each of the rectangular areas,
With the read image data of the (n + 1) th and subsequent pages of the sheet as a detection target of character deterioration, the character pixel ratio of each rectangular area calculated in the read image data is calculated in the read image data of the first to nth pages of paper. When the difference between the character area included in the rectangular area and the font information matches the character pixel rate of the reference that is stored in the storage unit and is outside the allowable range, character deterioration is detected. An image forming apparatus that performs optimization is provided.

According to the invention described in claim 2 ,
The control unit includes:
When the same image is formed on a plurality of pages of paper by the image forming unit, all rectangular areas are extracted from read image data of any one of pages 1 to n or all pages, and the reference character pixels are extracted. Rate calculation target,
When different images are formed on a plurality of pages of paper by the image forming unit, one or a plurality of rectangular areas having the same font information in each page are extracted from the read image data of the first to n pages, and 2. The image forming apparatus according to claim 1 , wherein the character pixel ratio is calculated.

According to the invention described in claim 3 ,
The control unit determines, in each rectangular area, a representative pixel value of the character area, a representative pixel value of the background area thereof, and a threshold located between the representative pixel values, and determines a pixel of each pixel in the rectangular area. A pixel of a character formed in the rectangular area is determined by comparing the value with the determined threshold value, and a ratio of the number of pixels of the character to all pixels in the rectangular area is calculated as the character pixel ratio. An image forming apparatus according to claim 1 or 2 , is provided.

According to the invention described in claim 4 ,
The control unit acquires attribute information and font information added to the original image data of the page on which the character deterioration is to be detected, and the attribute information is a character area indicating a character attribute, and the font information Is searched for a character area that matches the font information stored together with the reference character pixel rate, and if there is a corresponding character area, each rectangle for calculating the character pixel rate from the read image data to include the character area the image forming apparatus according to any one of claims 1 to 3, characterized in that extracting a region is provided.

According to the invention described in claim 5 ,
The control unit may determine the size of the rectangular area according to a size of a character area in which the attribute information indicates a character attribute, or a font type and a font size indicated by the font information. An image forming apparatus according to any one of Items 1 to 4 , is provided.

According to the invention described in claim 6 ,
The control unit executes the optimization of the image when the difference between the character pixel rate of the reference and the character pixel rate of the reference is out of an allowable range in the read image data of one page is equal to or more than a certain number. An image forming apparatus according to any one of claims 1 to 5 , characterized in that:

According to the invention described in claim 7 ,
Optimization of the image, the image line width, provides an image forming apparatus according to any one of claims 1 to 6, characterized in that at least one optimization of the density characteristics and maximum density Is done.

According to the invention described in claim 8 ,
Forming an image on paper based on the original image data by the image forming unit;
An image reading unit that reads a sheet surface on which the image is formed to generate read image data;
Analyzing a read image data by a control unit, and performing optimization of an image formed by the image forming unit,
Performing the optimization of the image,
The position of a character area is determined for each character based on the attribute information and font information of the character added to the original image data, and one or more rectangles are formed so as to include one or more character areas and their background areas. Extracting an area from the read image data;
Calculating a character pixel ratio formed in each of the extracted rectangular regions;
Immediately after executing the image optimization, the character pixel rate of each rectangular area calculated in the read image data of the first to n-th sheets on which the image is formed by the image forming unit is defined as the character pixel rate of the reference. Storing in a storage unit together with font information of a character area included in each rectangular area;
With the read image data of the (n + 1) th and subsequent pages of the sheet as a detection target of character deterioration, the character pixel ratio of each rectangular area calculated in the read image data is calculated in the read image data of the first to nth pages of paper. When the difference between the character area included in the rectangular area and the font information matches the character pixel rate of the reference that is stored in the storage unit and is outside the allowable range, character deterioration is detected. Performing an optimization;
And a method for optimizing an image.

  ADVANTAGE OF THE INVENTION According to this invention, the deterioration of a character can be easily detected and the image can be optimized at the timing when the deterioration occurs.

FIG. 1 is a front view illustrating a schematic configuration of an image forming apparatus according to an embodiment. FIG. 2 is a block diagram illustrating a configuration of the image forming apparatus for each function. 9 is a flowchart illustrating a processing procedure when the image forming apparatus executes image optimization. FIG. 7 is a diagram illustrating a rectangular area extracted from read image data based on attribute information and font information added to original image data. 9 shows an example of a rectangular area extracted to include a plurality of character areas.

  Hereinafter, embodiments of an image forming apparatus and an image optimizing method of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration of an image forming apparatus G according to the present embodiment.
As shown in FIG. 1, the image forming apparatus G includes an image forming unit 20 that forms an image on a sheet, and an image reading unit 30 that reads the surface of the sheet.

FIG. 2 illustrates a main configuration of the image forming apparatus G for each function.
As shown in FIG. 2, the image forming apparatus G includes a control unit 11, a storage unit 12, an operation unit 13, a display unit 14, a communication unit 15, an image generation unit 16, an image reading unit 17, an image memory 18, an image processing unit. 19, an image forming unit 20 and an image reading unit 30.

The control unit 11 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like, and controls each unit by reading and executing various programs from the storage unit 12.
For example, the control unit 11 causes the image processing unit 19 to perform image processing on the original image data generated by the image generation unit 16 or the image reading unit 17 and held in the image memory 18, and converts the original image data into the original image data after the image processing. The image forming unit 20 forms an image on a sheet based on the image.

The control unit 11 analyzes the read image data obtained by reading the sheet surface after the image formation by the image reading unit 30 and optimizes the image formed by the image forming unit 20.
The optimization of an image refers to an adjustment for accurately and stably reproducing an image. Examples of such adjustment include adjustment of line width, density characteristics, maximum density, and the like.

The storage unit 12 stores programs that can be read by the control unit 11, files used when executing the programs, and the like. As the storage unit 12, a large-capacity memory such as a hard disk can be used.
For example, the storage unit 12 stores a reference character pixel ratio and font information of each character such as a hiragana and an alphabet.

  The operation unit 13 generates an operation signal according to a user operation and outputs the operation signal to the control unit 11. As the operation unit 13, a keypad, a touch panel integrated with the display unit 14, or the like can be used.

  The display unit 14 displays an operation screen or the like according to an instruction from the control unit 11. As the display unit 14, an LCD (Liquid Crystal Display), an OELD (Organic Electro Luminescence Display), or the like can be used.

The communication unit 15 communicates with an external device on the network, for example, a user terminal, a server, another image forming device, or the like.
The communication unit 15 receives, from a user terminal via a network, vector data in which an instruction to form an image is described in a page description language (PDL).

  The image generation unit 16 performs a rasterization process on the vector data received by the communication unit 15 to generate bitmap format original image data. In the original image data, each pixel has four color pixel values of C (cyan), M (magenta), Y (yellow), and K (black). The pixel value is a data value representing the shading of the image. For example, an 8-bit data value represents shading of 0 to 255 gradations.

When generating the original image data, the image generating unit 16 generates attribute information indicating the attribute of each pixel of the original image data, and adds (tags) the attribute information to the original image data.
For example, the image generation unit 16 determines the attribute of each pixel of an image such as a kana, an alphabet, and a number, which is drawn in accordance with a character code described in vector data, as a character (Text), and outputs the attribute such as DXF, SVG, or WMF. The attribute of each pixel of an image such as a ruled line, a polygon, or a circle drawn according to the description in the vector format is determined as a graphic. Further, the image generation unit 16 determines the attribute of an image such as a photograph drawn in accordance with a file format such as JPEG as a photograph (Image).

When generating the original image data, the image generation unit 16 generates font information of characters in the original image data and adds the font information to the original image data.
For example, the image generating unit 16 generates information such as a character code, a font type, a font size, a color, and a density of a character described in vector data as font information. The character code is an identification code individually assigned to each character such as Unicode, JIS code and the like.

  The image reading unit 17 includes an automatic document feeder, a scanner, and the like, reads a document surface set on a document table, and generates bitmap original image data. In the original image data generated by the image reading unit 17, each pixel has a pixel value of three colors of R (red), G (green), and B (blue). This original image data is color-converted into original image data having pixel values of four colors C, M, Y, and K by a color conversion unit (not shown).

  The image memory 18 is a buffer memory that temporarily stores original image data generated by the image generation unit 16 or the image reading unit 17. As the image memory 18, a DRAM (Dynamic RAM) or the like can be used.

  The image processing unit 19 reads the original image data from the image memory 18 and performs layout processing such as image rotation, enlargement, reduction, page number addition, page aggregation, thinning processing, density correction processing, pseudo halftone Various image processing such as halftone processing for reproducing the image is performed.

The image forming unit 20 forms an image composed of four colors of C, M, Y and K on a sheet according to the pixel values of the four colors of each pixel of the original image data processed by the image processing unit 19. .
As shown in FIG. 1, the image forming section 20 includes four writing units 21, an intermediate transfer belt 22, a secondary transfer roller 23, a fixing device 24, and a paper feed tray 25.

  The four writing units 21 are arranged in series (tandem) along the belt surface of the intermediate transfer belt 22, and form images of C, M, Y, and K colors. Each writing unit 21 has the same configuration except that the color of the image to be formed is different. As shown in FIG. 1, the optical scanning device 2a, photoconductor 2b, developing unit 2c, charging unit 2d, cleaning unit 2e, and primary unit A transfer roller 2f is provided.

At the time of image formation, each writing unit 21 charges the photoconductor 2b by the charging unit 2d, and then scans the photoconductor 2b with a light beam emitted by the optical scanning device 2a based on the original image data, and forms an electrostatic latent image. To form When a color material such as toner is supplied and developed by the developing unit 2c, an image is formed on the photoconductor 2b.
The images formed on the photoconductors 2b of the four writing units 21 are sequentially transferred (primary transfer) onto the intermediate transfer belt 22 by the respective primary transfer rollers 2f. Thus, an image of each color is formed on the intermediate transfer belt 22. After the primary transfer, the coloring material remaining on the photoconductor 2b is removed by the cleaning unit 2e.

The image forming unit 20 feeds the paper from the paper feed tray 25, transfers the image from the intermediate transfer belt 22 onto the paper by the secondary transfer roller 23 (secondary transfer), and heats the paper by the fixing device 24. Pressure is applied to perform a fixing process.
When an image is formed on both sides of a sheet, the sheet is conveyed to the conveyance path 26, turned over, and then conveyed to the secondary transfer roller 23 again.

The image reading unit 30 reads a sheet surface on which an image is formed in the image forming unit 20, and generates read image data in a bitmap format.
As the image reading unit 30, a line sensor or an area sensor using an image sensor such as a CCD (Charge Coupled Device) can be used.

  The image forming apparatus G detects character deterioration while forming an image on a sheet of a plurality of pages by executing a job, and optimizes the image at the timing when the deterioration is detected, thereby reducing the deterioration of the character. Reproducibility can be restored immediately.

FIG. 3 shows a processing procedure when the image forming apparatus G executes image optimization.
As shown in FIG. 3, in the image forming apparatus G, the control unit 11 executes optimization of an image formed by the image forming unit 20 (Step S1).
It is preferable that the optimization of the image to be performed is optimization of at least one of the line width, the density characteristics, and the maximum density of the image, because the reproducibility of characters is improved.

When optimizing the line width of an image, the control unit 11 adjusts the thinning intensity used by the image processing unit 19 for thinning the original image data. The thinning process is a process of reducing the pixel value of a contour pixel of a line forming a character or the like, for example, and the amount by which the pixel value is reduced is adjusted by the thinning intensity.
The control unit 11 causes the image forming unit 20 to form a plurality of line images having different line widths as test patterns on a sheet, and causes the image reading unit 30 to read the sheet surface. The control unit 11 analyzes the obtained read image data, measures the line width of each line image, and determines the line width formed by the image forming unit 20 according to the difference between the measured value of the line width and the target value. The thinning intensity is determined so as to be a target value. The control unit 11 optimizes the line width of the image by updating the thinning intensity used by the image processing unit 19 to the determined thinning intensity.

When optimizing the density characteristics of an image, the control unit 11 updates the conversion table used by the image processing unit 19 for the density correction processing of the original image data. The conversion table is a table in which the input values are associated with the output values representing the corrected densities so that the density characteristics of the image become the target density characteristics. Is converted into a pixel value after density correction by this conversion table.
The control unit 11 causes the image forming unit 20 to form a plurality of patches having different densities stepwise on a sheet as a test pattern, and causes the image reading unit 30 to read the sheet surface. The control unit 11 analyzes the obtained read image data, and according to the difference between the density of each patch and its target value, the density characteristic of the image formed by the image forming unit 20 becomes the target density characteristic. Create a conversion table that defines input values and output values. The control unit 11 optimizes the density characteristics of the image by updating the conversion table used by the image processing unit 19 to a newly created conversion table.

When optimizing the maximum density of the image, the control unit 11 adjusts the set value of the image forming unit 20 that affects the maximum density of the image, such as the set value of the potential of the developing sleeve.
The control unit 11 causes the image forming unit 20 to form a patch having the maximum density as a test pattern by changing a set value such as the potential of the developing sleeve, and causes the image reading unit 30 to read the paper surface. The control unit 11 analyzes the obtained read image data and specifies a patch when the patch density matches the target maximum density among the patches. The density of each patch formed on the photoreceptor 2b or the intermediate transfer belt 22 instead of on the paper may be measured by a density sensor or the like. The control unit 11 optimizes the maximum density of the image by updating the set value such as the potential of the developing sleeve of the image forming unit 20 to the set value at the time of forming the specified patch.

  Immediately after performing the optimization, the image processing unit 19 performs necessary image processing on the original image data generated by the image generation unit 16 or the image reading unit 17 in response to the job execution instruction. At this time, the image processing unit 19 performs the thinning process and the density correction process using the thinning intensity and the conversion table optimized by the control unit 11. As a result, an image whose density has been optimized so as to obtain the target line width and density characteristics can be obtained. The image forming unit 20 forms an image on a sheet based on the original image data after the image processing (Step S2). At this time, since the set values such as the potential of the developing sleeve are optimized, an image whose maximum density is optimized to match the target maximum density is obtained.

The image reading section 30 reads the sheet surface on which the image is formed by the image forming section 20, and generates read image data (Step S3).
If the read sheet is the first to n-th page sheets immediately after optimizing the image (step S4: N), the control unit 11 analyzes the obtained read image data to determine the character pixel ratio of the reference. Is calculated (step S5). If the number n of pages for obtaining the reference character pixel rate is a positive number, it can be arbitrarily determined within a range where image quality does not deteriorate.

  First, the control unit 11 acquires attribute information and font information of the character added to the original image data from the original image data of the same page as the read image data. Then, the control unit 11 determines, for each character, the position of the character area in which the acquired attribute information indicates the attribute of the character and the font information indicates the same character code. The control unit 11 extracts one or a plurality of rectangular areas from the read image data so as to include one or more character areas and its background area, and calculates a character pixel rate formed in each rectangular area.

FIG. 4 illustrates a process of extracting a rectangular area.
As shown in FIG. 4, original image data 50 has attribute information 51 and character font information 52 added thereto. Note that the hatched portion in the attribute information 51 indicates a region where the attribute is a character.
The control unit 11 determines an area circumscribing a pixel group in which the attribute information 51 indicates a character attribute and the font information 52 indicates the same character code as a character area 61 of one character. The control unit 11 extracts a rectangular area 62 from the read image data 60 so as to include the character area 61 of each character and its background area according to the determined position of the character area 61 of each character.

The size of the M × N pixels of the rectangular area 62 is preferably larger than that of the character area 61 in consideration of a shift of the paper position at the time of reading.
The control unit 11 may determine the size of the M × N pixels of the rectangular area 62 according to the size of the character area 61 in which the attribute information 51 indicates the attribute of the character, or the font type and the font size indicated by the font information. it can.
For example, the control unit 11 can determine the size of the rectangular area 62 to be 10 pixels larger than the character area 61 in which the attribute information indicates the attribute of the character. If the font type indicated by the font information is Gothic and the font size is 14 pt, the control unit 11 may determine the size of the rectangular area 62 to be the same size as the rectangular area circumscribing a 15 pt character larger by 1 pt. it can.

In addition, the control unit 11 can extract one rectangular area 62 so as to include a character area 61 of one character as shown in FIG. 4, or a character area of a plurality of characters in units of a character string, a sentence, or the like. One rectangular area 62 can be extracted so as to include 61.
FIG. 5 shows an example of one rectangular area 63 extracted by determining the size of M × N pixels so as to include the character area 61 of three characters in the read image data 60 shown in FIG.

  The control unit 11 determines, as the representative pixel value of the character, the representative pixel value of the character region in which the attribute information indicates the attribute of the character in each of the extracted rectangular regions. The representative pixel value of the character may be an average value of the pixel values of each pixel in the character area, or may be any one of the pixel values. Similarly, the control unit 11 determines the representative pixel value of the background area in which the attribute information indicates the attribute other than the character in the rectangular area as the representative pixel value of the background.

  Next, the control unit 11 determines a threshold value between the calculated representative pixel values of the character and the background, and stores the determined representative pixel value and the threshold value of the character and the background in the storage unit 12. The threshold value can be arbitrarily determined as long as it is a value between the representative pixel values. For example, the threshold value can be determined as an average value of the representative pixel values of the character and the background.

The threshold can also be determined by creating a histogram.
When determining by the histogram, the control unit 11 creates a histogram of the pixel values of each pixel in the character area in the rectangular area, and determines the peak value in this histogram as the representative pixel value of the character. Similarly, the control unit 11 creates a histogram of the pixel values of each pixel in the background area, determines the peak value in this histogram as the representative pixel value of the background, and determines the value between the determined character and the representative pixel value of the background. Determines the threshold.

  The control unit 11 determines whether each pixel is a pixel of a character formed on the paper or a pixel of a background other than the character by comparing the pixel value of each pixel in the rectangular area with a threshold value. Specifically, when the representative pixel value of the character is larger than the representative pixel value of the background, the control unit 11 determines a pixel whose pixel value is equal to or larger than the threshold value as a pixel of the character, and determines a pixel whose pixel value is smaller than the threshold value as a background pixel. Determined as a pixel. On the other hand, when the representative pixel value of the character is smaller than the representative pixel value of the background, the control unit 11 determines a pixel whose pixel value is equal to or less than the threshold as a pixel of the character, and determines a pixel whose pixel value is larger than the threshold as a pixel of the background. I do.

After determining the pixels of the character, the control unit 11 calculates the ratio of the number of pixels of the character in all the pixels in each rectangular region as the character pixel ratio of each rectangular region. The control unit 11 stores the calculated character pixel rate of each rectangular area as a reference character pixel rate in the storage unit 12 together with the font information of the character area included in each rectangular area.
When a plurality of reference character pixel ratios are calculated for the same character having the same font information from one page of read image data, the control unit 11 stores the average value of each character pixel ratio in the storage unit 12 together with the font information. May be.

In calculating the representative pixel value of the character and the background, the threshold value, and the character pixel ratio, it is possible to use the pixel value of any one of the C, M, Y, and K pixel values of each pixel. it can.
For one color to be used, for example, the maximum pixel value and the minimum pixel value of each color may be determined in the extracted rectangular area, and the color having the largest difference may be determined as one color, or the color of the character included in the font information and the complementary color may be determined. One color that is related may be determined. By determining such a single color, the detection accuracy of character deterioration is improved.

In addition, in calculating the representative pixel value of the character and the background, the threshold value, and the character pixel ratio, a pixel value of one color obtained by integrating each of C, M, Y, and K can be used.
For example, the pixel values of four colors may be simply added to be converted to pixel values of one color, or the pixel values of each color may be weighted according to the visual sensitivity of each color, and then added together to obtain a pixel value of one color. It may be converted to a value.

When the image forming unit 20 forms the same image on a plurality of pages of paper, the control unit 11 refers to any one of pages 1 to n or all rectangular areas extracted from the read image data of all pages. In the case where different images are formed on a plurality of pages of paper as a calculation target of the character pixel ratio, one or a plurality of rectangular regions having common font information in each page are extracted from the read image data of the first to nth pages. It is preferable that the character pixel ratio is calculated.
This makes it possible to efficiently detect the deterioration of characters.

In the case where the same image is formed, when all the rectangular areas are extracted from the read image data of all pages 1 to n and the character pixel ratio of the reference is calculated, each page or each page The average value of the character pixel ratio of the reference whose font information matches between them can be stored as the character pixel ratio of the reference of the font information.
Similarly, in the case of forming different images, the character pixel ratio of the reference whose font information matches within each of pages 1 to n or between pages is averaged, and the obtained average value is used as the reference character of the font information. It can be stored as a pixel rate.

  On the other hand, when the read sheet is the sheet after the (n + 1) th page (step S4: Y), the control unit 11 sets the read image data of the sheet surface acquired from the image reading unit 30 as a detection target of the character deterioration. The character pixel ratio is calculated (step S6). Specifically, in the same manner as the character pixel ratio of the reference described above, attribute information and font information added to the original image data of the page for which character deterioration is to be detected are obtained, and one or more characters are read from the read image data. One or more rectangular areas are extracted so as to include the character area and its background area, and the character pixel ratio of each rectangular area is calculated. Since the character pixel rate varies depending on the size of the rectangular area, the method for determining the size of the rectangular area is the same as the method for calculating the character pixel rate without referent.

Before extracting the rectangular area from the read image data, the control unit 11 searches for a character area in which the attribute information indicates the attribute of the character, and the character pixel rate of the reference matches the font information. When there is a character area, each rectangular area for calculating the character pixel ratio may be extracted from the read image data so as to include the character area.
Thus, the character pixel ratio can be calculated only for characters for which the reference character pixel ratio is prepared, and character deterioration can be efficiently detected.

  The control unit 11 acquires from the storage unit 12 the character pixel ratio of the reference whose font information matches the extracted rectangular region, and compares it with the calculated character pixel ratio of each rectangular region. As a result of the comparison, when the difference between the calculated character pixel ratio and the reference character pixel ratio is out of the allowable range (step S7: Y), the control unit 11 detects the deterioration of the character and executes the image optimization ( Step S8). For example, if the allowable range is -10 to + 10%, and the difference between the calculated character pixel ratio and the reference character pixel ratio is + 12%, the control unit 11 determines that the difference is outside the allowable range. The optimization of the image has the same processing content as the processing in step S1, and is preferably at least one of the line width, the density characteristics, and the maximum density of the image.

When a plurality of rectangular areas are extracted from the read image data of one page, the control unit 11 determines that there is at least one rectangular area having a difference from the character pixel ratio of the reference outside the allowable range in one page. The optimization of the image may be performed in a certain case, or may be performed in a case where there is a certain number or more.
When the execution condition of the optimization is that at least one rectangular area outside the allowable range is set as the execution condition of the optimization, high image reproducibility can always be maintained. The frequency can be suppressed and productivity can be prioritized.

  After executing the image optimization, if the read sheet is not the last page (step S9: N), the process returns to step S2, and the above-described process is repeated for the next page. If the read sheet is the last page (step S9: Y), the process ends.

  On the other hand, if the difference between the calculated character pixel ratio and the reference character pixel ratio is within the allowable range (step S7: N), the control unit 11 determines that the deterioration of the character is not detected and optimizes the image. Instead, the process proceeds to step S9.

As described above, the image forming apparatus G according to the present embodiment reads the image forming unit 20 that forms an image on a sheet and the sheet surface on which the image is formed by the image forming unit 20 based on the original image data. An image reading unit 30 that generates read image data; a control unit 11 that analyzes the read image data to execute optimization of an image formed by the image forming unit 20; A storage unit 12 for storing font information.
The control unit 11 determines the position of the character area for each character based on the attribute information and the font information of the character added to the original image data, and sets one or more character areas and the background area so as to include one or more character areas. Alternatively, a plurality of rectangular areas are extracted from the read image data, and a character pixel ratio formed in each rectangular area is calculated. Further, the control unit 11 detects the deterioration of the character when the difference between the calculated character pixel ratio of each rectangular area and the character pixel ratio of the reference whose font information matches is out of an allowable range, and detects the deterioration of the character. Perform optimization.

Character degradation is detected based on the character pixel ratio calculated using attribute information and font information, so even if it is not high-resolution read image data, it is also difficult to detect line width changes. Even if it is a character or the like, the deterioration of the character can be detected accurately and easily. In addition, it is possible to detect the deterioration of the characters during the continuous image formation, and to avoid a decrease in productivity.
Since the deterioration of the character is detected when the difference of the character pixel ratio from the reference falls outside the allowable range, the image can be optimized at the timing when the deterioration occurs.

The above embodiment is a preferred example of the present invention, and the present invention is not limited to this. Changes can be made as appropriate without departing from the spirit of the present invention.
For example, in the above-described embodiment, the read image data of pages 1 to n immediately after the optimization of the image is set as the reference character pixel ratio calculation target, and the read image data of page n + 1 and subsequent pages is degraded by the character deterioration. Is detected.
The present invention is not limited to this. The character pixel ratio of the reference of each character is stored in advance in the storage unit 12 in association with the font information of the character, and the reading of all pages is performed regardless of whether or not the image has been optimized. The image data may be a detection target of character deterioration.

  In addition, as a computer-readable medium of a program for causing a computer such as the control unit 11 to execute the above processing procedure, a non-volatile memory such as a ROM or a flash memory, or a portable recording medium such as a CD-ROM may be used. Is possible. As a medium for providing program data via a communication line, a carrier wave (carrier wave) can also be applied.

G image forming apparatus 11 control unit 12 storage unit 16 image generation unit 17 image reading unit 19 image processing unit 20 image forming unit 30 image reading unit

Claims (8)

An image forming unit that forms an image on paper based on the original image data;
An image reading unit that reads a sheet surface on which an image is formed by the image forming unit and generates read image data;
A control unit that analyzes the read image data and executes optimization of an image formed by the image forming unit;
A storage unit for storing a character pixel ratio and font information of a reference of each character,
The control unit includes:
The position of a character area is determined for each character based on the attribute information and font information of the character added to the original image data, and one or more rectangles are formed so as to include one or more character areas and their background areas. Extracting a region from the read image data, calculating a character pixel ratio formed in each rectangular region,
The character pixel ratio of each rectangular area calculated in the read image data of the 1st to nth pages of paper on which the image is formed by the image forming unit immediately after executing the image optimization is defined as the character pixel ratio of the reference. Stored in the storage unit together with font information of a character area included in each of the rectangular areas,
With the read image data of the (n + 1) th and subsequent pages of the sheet as the detection target of the character deterioration, the character pixel ratio of each rectangular area calculated in the read image data is calculated in the read image data of the first to nth pages of the sheet. When the difference between the character area included in the rectangular area stored in the storage unit and the character pixel rate of the reference in which font information matches font information is out of an allowable range, character deterioration is detected, and An image forming apparatus that performs optimization . The control unit includes:
When the same image is formed on a plurality of pages of paper by the image forming unit, all rectangular areas are extracted from read image data of any one of pages 1 to n or all pages, and the reference character pixels are extracted. Rate calculation target,
When different images are formed on a plurality of pages of paper by the image forming unit, one or a plurality of rectangular areas having the same font information in each page are extracted from the read image data of the first to n pages, and The image forming apparatus according to claim 1 , wherein the character pixel ratio is calculated. The control unit determines, in each rectangular area, a representative pixel value of the character area, a representative pixel value of the background area thereof, and a threshold located between the representative pixel values, and determines a pixel of each pixel in the rectangular area. A pixel of a character formed in the rectangular area is determined by comparing the value with the determined threshold value, and a ratio of the number of pixels of the character to all pixels in the rectangular area is calculated as the character pixel ratio. the image forming apparatus according to claim 1 or 2, characterized in that. The control unit acquires attribute information and font information added to the original image data of the page on which the character deterioration is to be detected, and the attribute information is a character area indicating a character attribute, and the font information Is searched for a character area that matches the font information stored together with the reference character pixel rate, and if there is a corresponding character area, each rectangle for calculating the character pixel rate from the read image data to include the character area the image forming apparatus according to any one of claims 1 to 3, characterized in that to extract the region. The control unit may determine the size of the rectangular area according to a size of a character area in which the attribute information indicates a character attribute, or a font type and a font size indicated by the font information. Item 5. The image forming apparatus according to any one of Items 1 to 4 . The control unit executes the optimization of the image when the difference between the character pixel rate of the reference and the character pixel rate of the reference is out of an allowable range in the read image data of one page is equal to or more than a certain number. the image forming apparatus according to any one of claims 1 to 5, wherein. Optimization of the image, the image line width, an image forming apparatus according to any one of claims 1 to 6, characterized in that at least one optimization of the density characteristics and maximum density. Forming an image on paper based on the original image data by the image forming unit;
An image reading unit that reads a sheet surface on which the image is formed to generate read image data;
Analyzing a read image data by a control unit, and performing optimization of an image formed by the image forming unit,
Performing the optimization of the image,
The position of a character area is determined for each character based on the attribute information and font information of the character added to the original image data, and one or more rectangles are formed so as to include one or more character areas and their background areas. Extracting an area from the read image data;
Calculating a character pixel ratio formed in each of the extracted rectangular regions;
Immediately after executing the image optimization, the character pixel rate of each rectangular area calculated in the read image data of the first to n-th sheets on which the image is formed by the image forming unit is defined as a reference character pixel rate. Storing in a storage unit together with font information of a character area included in each rectangular area;
With the read image data of the (n + 1) th and subsequent pages of the sheet as a detection target of character deterioration, the character pixel ratio of each rectangular area calculated in the read image data is calculated in the read image data of the first to nth pages of paper. When the difference between the character area included in the rectangular area stored in the storage unit and the character pixel rate of the reference in which font information matches font information is out of an allowable range, character deterioration is detected, and Performing an optimization;
A method for optimizing an image, comprising:

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