JP6131613B2 - Image forming apparatus and image processing method - Google Patents

Description

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

  In general, the line width of characters formed by an electrophotographic image forming apparatus may be thicker than the original line width due to factors such as dot gain and toner scattering. Is being processed. By thinning processing that reduces the pixel value of the outline of a character, it is possible to suppress an increase in line width due to image formation.

In the thinning process, in the case of binary image data, all the pixel values of the contour are reduced to erase the contour itself, thereby realizing thinning (see, for example, Patent Document 1). On the other hand, in the case of multivalued image data, the line width is adjusted by partially reducing the pixel value of the contour (see, for example, Patent Document 2). The intensity of thinning can be adjusted depending on how much the pixel value is reduced.
Conventionally, the adjustment of the thinning strength has been manually set by the user from among stepwise strengths prepared in advance, for example, five levels of strength.

JP 2009-212376 A JP 2005-341249 A

However, the line width may fluctuate depending on the conditions at the time of image formation, for example, the maximum density or the type of paper, and the line may not be thinned with the intensity set by the user.
In addition, when the maximum density is changed, the line width after image formation may vary depending on whether it is a vertical line or a horizontal line due to noise or the like.

  An object of the present invention is to stabilize the line width after thinning.

According to the invention of claim 1,
Analyzing the image data, the contour detection unit for determining the edge pixel of the contour pixel and the contour pixel of the character or figure,
A thinning unit that reduces the pixel value of the contour pixel in accordance with the edge direction of the contour pixel and thins the character or figure;
In accordance with image forming conditions, an intensity adjustment unit that adjusts the pixel value after thinning of the contour pixels so that the line width after thinning becomes an expected value;
An image forming apparatus is provided.

According to invention of Claim 2,
Analyzing the image data, a contour detection unit that determines a contour pixel of a character or a figure and an edge direction of the contour pixel;
A thinning unit that reduces the pixel value of the contour pixel in accordance with the edge direction of the contour pixel and thins the character or figure;
Depending on the image forming condition and whether the contour pixel is a vertical or horizontal contour pixel, the vertical and horizontal contour pixels are thinned so that the line width after thinning becomes an expected value. An intensity adjustment unit for adjusting the pixel value of
An image forming apparatus is provided.

According to invention of Claim 3 ,
The image forming condition is maximum density or paper type.
An image forming apparatus according to claim 1 or 2 is provided.

According to invention of Claim 4 ,
Analyzing image data and determining a contour pixel of a character or a figure and an edge direction of the contour pixel;
A thinning step of reducing the pixel value of the contour pixel according to the edge direction of the contour pixel, and thinning the character or figure,
According to the image forming conditions, an intensity adjustment step of adjusting the pixel value after thinning of the contour pixels so that the line width after thinning becomes an expected value;
An image processing method is provided.

According to the invention of claim 5 ,
Analyzing image data and determining a contour pixel of a character or figure and an edge direction of the contour pixel;
A thinning step of reducing the pixel value of the contour pixel according to the edge direction of the contour pixel, and thinning the character or figure,
Depending on the image forming condition and whether the contour pixel is a vertical or horizontal contour pixel, the vertical and horizontal contour pixels are thinned so that the line width after thinning becomes an expected value. An intensity adjustment step of adjusting the pixel value of
An image processing method is provided.

  According to the present invention, it is possible to suppress fluctuations in the line width that is thinned after image formation, and it is possible to stabilize the line width after thinning. Therefore, it is possible to reproduce the image-formed character or graphic with the expected line width.

1 is a functional block diagram of an image forming apparatus according to the present embodiment. It is a functional block diagram of the image processing apparatus of FIG. It is a figure which shows 3x3 pixel. (A) It is a figure which shows the correspondence of developing potential and line | wire width. (B) It is a figure which shows the correspondence of laser power and line | wire width. 6 is a flowchart showing a processing procedure when the image processing apparatus adjusts the intensity of thinning according to image forming conditions after thinning. (A) It is a figure which shows each pixel of the character of T and its background. (B) It is a figure which shows the processing result which thinned the outline of the character of (a). (C) It is a figure which shows the processing result which adjusted the intensity | strength of the thinning of the outline of the character of (b) according to image formation conditions. (A) It is a figure which shows the correspondence of the developing potential and the line | wire width of a vertical line and a horizontal line. (B) It is a figure which shows the correspondence of a laser power and the line | wire width of a vertical line and a horizontal line. It is a flowchart which shows the process sequence when an image processing apparatus adjusts the intensity | strength of thinning according to whether it is a vertical line or a horizontal line after thinning. (A) It is a figure which shows each pixel of the character of T and its background. (B) It is a figure which shows the processing result which thinned the outline of the character of (a). (C) It is a figure which shows the processing result which adjusted the intensity | strength of the thinning of the outline of the character of (b) by the vertical line or the horizontal line.

  Embodiments of an image forming apparatus and an image processing method of the present invention will be described below with reference to the drawings.

FIG. 1 is a functional block diagram of an image forming apparatus G according to the present embodiment.
As shown in FIG. 1, the image forming apparatus G includes a control unit 1, a storage unit 2, an operation unit 3, a display unit 4, a communication unit 5, a print controller 6, a scanner 7, an image memory 8, an image processing device 9, and an image processing device 9. A forming unit 10 is provided.

The control unit 1 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like. The control unit 1 reads a program stored in the storage unit 2 and controls each unit of the image forming apparatus G according to the program.
For example, the control unit 1 causes the image processing device 9 to perform image processing on the image data and causes the image forming unit 10 to form an image.

  The storage unit 2 stores programs, files, and the like that can be read by the control unit 1. As the storage unit 2, for example, a storage medium such as a hard disk or a ROM (Read Only Memory) can be used.

The operation unit 3 includes an operation key, a touch panel configured integrally with the display unit 4, and the like, and outputs operation signals corresponding to these operations to the control unit 1.
The display unit 4 displays an operation screen and the like according to instructions from the control unit 1.
The communication unit 5 communicates with a server on the network in accordance with an instruction from the control unit 1.

  The print controller 6 includes a communication unit, receives PDL (Page Description Language) data from a computer on the network, rasterizes the PDL data, and generates bitmap format image data. The print controller 6 generates image data of four colors of C (cyan), M (magenta), Y (yellow), and K (black). The generated image data is output to the image memory 8 and held.

The print controller 6 generates attribute data indicating the attribute of each pixel during the rasterization process. The attribute data is output together with the image data.
The attributes include text, graphics, and images. The figure is, for example, a circle, a polygon, an arrow, a line, a ruled line, or the like. The print controller 6 sets the attribute of the pixel corresponding to each object of character, graphic, and photograph to the attribute of character, graphic, and photo, respectively.

  The scanner 7 reads an original and generates image data of three colors of R (red), G (green), and B (blue). The generated image data is output to the image memory 8 and held.

  The image memory 8 is a memory that holds image data. As the image memory 8, a DRAM (Dynamic Random Access Memory) or the like can be used.

The image processing device 9 performs color conversion on the R, G, B image data generated by the scanner 7 and writes the obtained C, M, Y, K image data in the image memory 8.
The image processing device 9 compresses the C, M, Y, and K image data held in the image memory 8 and writes the compressed image data into the image memory 8, and in response to an image formation instruction from the control unit 1, the image data Is read from the image memory 8 and decompressed.
The image processing device 9 performs thinning processing and halftone processing on the image data and outputs the processed image data to the image forming unit 10.

The image forming unit 10 forms an image on a sheet based on the image data.
Specifically, the image forming unit 10 includes four sets of an exposure unit, a development unit, and a photoreceptor for each of C, M, Y, and K colors. The exposure unit exposes the charged and rotating photoconductor by optical scanning with a laser diode based on the image data. The developing unit supplies toner by a developing roller, and develops the electrostatic latent image formed on the photoconductor by exposure. The images of the respective colors formed on the four photoconductors in this way are transferred onto the paper in a superimposed manner via an intermediate transfer belt or the like, and fixed by a fixing device.

FIG. 2 is a functional block diagram of components that perform thinning processing and halftone processing in the image processing apparatus 9.
As shown in FIG. 2, the image processing apparatus 9 includes a contour detection unit 101, a thinning unit 102, an intensity adjustment unit 103, a contone processing unit 104, a halftone processing unit 105, an output selection unit 106, and a storage unit 107. Yes.

  The contour detection unit 101 analyzes the image data and determines the contour pixel of the character or figure and the edge direction of the contour pixel. An outline pixel is a pixel located in the outline of a character or a figure, and an edge direction is a direction from a pixel with a small pixel value toward a large pixel.

Specifically, the contour detection unit 101 inputs image data in units of 3 × 3 pixels, determines whether the pixel of interest is a contour pixel of a character with the pixel located at the center as the pixel of interest, and the contour pixel If it is, the edge direction is further determined.
FIG. 3 shows 3 × 3 pixels.
In FIG. 3, each pixel is represented as pixels 0 to 8. Pixel 4 is the target pixel.

When the attribute of the target pixel 4 indicated by the attribute data is a character or a figure, the contour detection unit 101 includes the target pixel 4 and the adjacent pixels 1, 7, 3, and 5 adjacent to the target pixel 4 in the vertical and horizontal directions. Differences SP [u], SP [d], SP [l] and SP [r] are calculated.
When the pixel values of the pixel of interest 4 and the adjacent pixels 1, 7, 3 and 5 are respectively expressed as C [4], C [1], C [7], C [3] and C [5], each difference SP [u], SP [d], SP [l] and SP [r] are expressed as follows.
SP [u] = C [4] -C [1]
SP [d] = C [4] -C [7]
SP [l] = C [4] -C [3]
SP [r] = C [4] -C [5]

  Next, the contour detection unit 101 compares SP [u] and SP [d], and compares SP [l] and SP [r]. As a result of the comparison, if SP [u] ≠ SP [d] or SP [l] ≠ SP [r], the contour detection unit 101 determines that the pixel of interest 4 is a character contour pixel.

When the edge directions in the main scanning direction and the sub-scanning direction are expressed as Px and Py, respectively, the contour detection unit 101 determines Px = + 1 when SP [l]> SP [r], and SP [l] <SP When [r], Px = −1 is determined, and when SP [l] = SP [r], Px = 0 is determined.
The contour detection unit 101 determines Py = + 1 when SP [u] <SP [d], and determines Py = −1 when SP [u]> SP [d], and SP [u ] = SP [d], Py = 0 is determined.

When the total edge direction of the pixel of interest is represented as P, the contour detection unit 101 determines the edge direction P as follows according to the combination of the edge direction Px in the main scanning direction and the edge direction Py in the sub-scanning direction. .
When Px = + 1 and Py = −1, P = 4
When Px = + 1 and Py = 0, P = 2
When Px = + 1 and Py = + 1, P = 7
When Px = 0 and Py = −1, P = 0
When Px = 0 and Py = + 1, P = 1
When Px = -1 and Py = -1, P = 6
When Px = -1 and Py = 0, P = 3
When Px = -1 and Py = + 1, P = 5

The following table shows the edge directions represented by P values 0-7. As shown in the table, the edge direction P is a total of eight directions including four directions in the up, down, left, and right directions and four oblique directions.

The thinning unit 102 reduces the pixel value of the contour pixel determined by the contour detection unit 101 according to the edge direction of the contour pixel, and thins the character or figure.
Specifically, the thinning unit 102 performs weighted averaging of the pixel value of the contour pixel and the pixel value of the adjacent pixel adjacent in the direction opposite to the edge direction of the contour pixel, and the obtained pixel value is calculated for the contour pixel. Output as a pixel value after thinning. For example, when the edge direction P of the contour pixel is P = 3 and the left direction, the thinning unit 102 uses the adjacent pixel located on the right side of the contour pixel for the weighted average.

When the pixel values of the contour pixel and the adjacent pixel are represented as C [OE] and C [PA], respectively, and the pixel value after thinning the contour pixel is represented as C [OEs], the thinning unit 102 obtains the pixel value C [ OEs] is calculated by the following equation.
C [OEs] = C [OE] × f / 100 + C [PA] × (100−f) / 100
Here, f is a thinning coefficient and can be appropriately determined within a range of 0 to 100%. Five levels of strengths 1 to 5 are prepared as the thinning strength, and f can be set according to the strength designated by the user via the operation unit 3. For example, f = 75% for strength 1, f = 60% for strength 2, f = 45% for strength 3, f = 30% for strength 4, 10% for strength 5 You only have to set it.

  Adjacent pixels in the direction opposite to the edge direction are background pixels and have a pixel value smaller than that of the contour pixel as the foreground. As shown in the calculation formula for C [OEs], the pixel value of the contour pixel can be reduced by merging (mixing) the pixel value of the adjacent pixel with the pixel value of the contour pixel.

The intensity adjusting unit 103 adjusts the pixel value after thinning of the contour pixel so that the line width after thinning becomes an expected value according to the image forming conditions of the image forming unit 10, and reduces the thinning intensity. adjust.
Specifically, the intensity adjusting unit 103 estimates the line width after image formation from the image forming conditions, calculates an adjustment value of the thinning intensity from an error between the estimated value of the line width and the expected value, and generates a contour pixel. The adjustment value is added to the pixel value after thinning. The intensity adjustment unit 103 acquires image forming conditions from the control unit 1.

Image forming conditions that affect the line width include maximum density, paper type, and the like.
For example, at the time of adjusting the maximum density, a patch image in which the maximum pixel value is set is formed by the image forming unit 10, and the development potential, laser power (MPC; MPC;) so that the measured density of the patch image becomes the target density. Etc.) is also adjusted. The developing potential refers to the potential (V) of the developing roller of the developing portion that is negatively charged by the application of voltage, and the laser power refers to the output energy (mW) of the laser diode in the exposed portion. The larger the absolute value of the developing potential and the larger the laser power, the more toner is on the paper and the density is increased. Due to these properties, the line width varies depending on the set value of the development potential and the laser power.

FIG. 4A shows the measurement result of the line width when a line test pattern having a line width of 2 pixels (42 μm when 1200 dpi) is formed with different development potentials.
As shown in FIG. 4A, the line width increases as the development potential increases (the development potential is a negative potential, so the absolute value is large). The expected value Wt of the line width is 42 μm, but the line width varies from the expected value Wt depending on the set value of the development potential.

FIG. 4B shows a measurement result of the line width when the same test pattern is formed with different laser powers.
As for the laser power, like the developing potential, the line width tends to increase as the laser power increases, and the line width varies from the expected value Wt of 42 μm depending on the set value of the laser power.

As described above, the storage unit 107 stores the correspondence between the image forming conditions and the line widths obtained by measurement in advance. The intensity adjusting unit 103 obtains an estimated value of the line width according to the image forming condition from the correspondence relationship stored in the storage unit 107. Since the line width fluctuates after image formation by the difference between the expected value and the estimated value of the line width, the intensity adjustment unit 103 adjusts the fluctuation value from both ends of the line. Calculate as follows.
Adjustment value (%) = 100% × {(expected value−estimated value) (μm) / 2} / 1 pixel width (μm)

  For example, the intensity adjusting unit 103 obtains an estimated value W1 of the line width corresponding to the set value V1 of the development potential from the correspondence shown in FIG. 4A, and subtracts the estimated value W1 from the expected value Wt. Ask for. For example, when the difference is −21 μm, the width of one pixel is 21 μm, and the intensity adjustment unit 103 adjusts −50% (−50 = 100 × {−21/2} / 21) from the above formula. Determine as value.

The intensity adjusting unit 103 obtains the estimated line width W2 from the laser power set value E1 from the correspondence shown in FIG. When the difference between the expected value Wt and the estimated value W2 is, for example, +10.5 μm, the width of one pixel is 21 μm. Therefore, the intensity adjustment unit 103 calculates + 25% (+ 25 = 100 × {+ 10.5 / 2} / 21) is determined as the adjustment value.
The intensity adjustment unit 103 adds the adjustment value −50% calculated according to the development potential and the adjustment value + 25% calculated according to the laser power to the pixel value after the thinning of the contour pixel. When the pixel value after thinning the contour pixel is 75%, the intensity adjustment unit 103 outputs 50% (50 = 75−50 + 25) as the pixel value of the contour pixel after adjustment.

The intensity adjusting unit 103 can adjust the intensity of thinning in the same way even when the image forming condition is the type of paper.
In the case of the type of paper, for example, the coated paper has good transferability and the line width tends to increase, and the line width may vary after image formation depending on the type. The intensity adjustment unit 103 obtains a measurement value of a line width when a line test pattern having a predetermined line width is formed on each type of paper, and determines each type of adjustment value. The intensity adjustment unit 103 stores the determined adjustment values in the storage unit 107, reads out adjustment values according to the type of paper used for image formation from the storage unit 107, and pixel values after thinning the contour pixels Add to.

Further, the expected value Wt of the line width may be different from the ideal line width.
For example, when the resolution of the image data is 1200 dpi, it is ideal that an image can be formed with a line width of 2 pixels and a line width of 42 μm. As described above, the expected value Wt can be set to 42 μm, which is the same as the ideal line width. However, the expected value Wt of the line width is prevented in order to prevent unintentional thinning and collapse of the shape of the character. Can also be 45 μm.

  The contone processing unit 104 performs contone processing on the image data adjusted by the intensity adjustment unit 103 and outputs the processed data to the output selection unit 106. The contone process is a process for outputting image data as it is.

  The halftone processing unit 105 performs halftone processing on the image data output from the thinning unit 102 and outputs the processed image data to the output selection unit 106. Examples of halftone processing include error diffusion processing and screen processing using a dither matrix.

  The output selection unit 106 selects and outputs the image data output from the contone processing unit 104 for the contour pixels determined by the contour detection unit 101 among the pixels of the image data. The output selection unit 106 outputs the image data output from the halftone processing unit 105 for each pixel other than the contour pixel.

  Since the halftone-processed image data is expressed in gradation by the density of dots, the outline of characters or figures tends to be unclear. On the other hand, in the image data subjected to the contone process, the pixel value of each pixel is directly reflected in the dot. Therefore, for the contour pixel, the contour of the character or figure can be emphasized more than the background region subjected to the screen processing by selecting the image data subjected to the contone processing.

The storage unit 107 stores a correspondence relationship between the development potential, the laser power, and the line width.
The storage unit 107 stores adjustment values for each paper type.

FIG. 5 is a flowchart showing a processing procedure when the image processing device 9 thins characters or figures and adjusts the thinning intensity according to the image forming conditions.
In the image processing device 9, as shown in FIG. 5, the contour detection unit 101 determines the contour pixel of a character or graphic and the edge direction of the contour pixel (step S1).
Next, the thinning unit 102 reduces the pixel value of the contour pixel determined by the contour detection unit 101 in accordance with the edge direction of the contour pixel, thereby thinning the character or figure (step S2).
The halftone processing unit 105 performs halftone processing on the image data in which characters or figures are thinned (step S3).

The intensity adjusting unit 103 estimates the line width after image formation according to the set value of the development potential (step S4). The intensity adjustment unit 103 determines an adjustment value of the thinning intensity from the difference between the expected value and the estimated value of the line width (step S5).
Similarly, the intensity adjusting unit 103 estimates the line width after image formation according to the set value of the laser power (step S6), and the adjustment value of the thinning intensity from the difference between the estimated value of the line width and the expected value. Is determined (step S7).

The intensity adjustment unit 103 adds each adjustment value determined according to the developing potential and the laser power to the pixel value after thinning of the contour pixel determined by the contour detection unit 101, and adjusts the thinning intensity. (Step S8).
The contone processing unit 104 performs contone processing on the image data adjusted by the intensity adjustment unit 103 and outputs the processed image data (step S9).

  If each pixel of the image data is a contour pixel determined by the contour detection unit 101, the output selection unit 106 outputs the image data output from the contone processing unit 104. Further, the output selection unit 106 outputs the image data output from the halftone processing unit 105 if it is a pixel other than the contour pixel determined by the contour detection unit 101 (step S10).

  The above-described processing procedure is an example in the case where the thinning intensity is adjusted according to the maximum density condition during image formation. When the image forming condition is a paper type, the thinning intensity can be adjusted by the same processing procedure except that an adjustment value corresponding to the paper type is acquired from the storage unit 107.

FIG. 6A to FIG. 6C show thinning processing results by the image processing apparatus 9.
FIG. 6A shows a letter T and each pixel of the background. The pixel value of the character portion has a maximum value of 100%, and the background pixel value has a minimum value of 0%. In addition, the arrow in FIG. 6A indicates the edge direction of the contour pixel determined by the contour detection unit 101.
When thinning is performed by the thinning unit 102, the pixel value of the adjacent pixel in the background located in the direction opposite to the edge direction is merged with the pixel value of the outline pixel of the character, as shown in FIG. The pixel value of the contour pixel is uniformly reduced.
When the estimated value of the line width estimated from the image forming conditions exceeds the expected value, the intensity adjustment unit 103 adds a negative adjustment value to the pixel value of the contour pixel. As a result, the pixel value of the contour pixel is further reduced as shown in FIG.
Since the line width after image formation is increased by the amount reduced by the adjustment value, a character thinned with a thinning coefficient f is finally obtained.

  As described above, according to the present embodiment, the image forming apparatus G analyzes the image data, determines the contour pixel of the character or figure and the edge direction of the contour pixel, and the contour pixel The pixel value is reduced according to the edge direction of the contour pixel, the thinning unit 102 for thinning a character or a figure, and the line width after thinning becomes an expected value according to the image forming conditions. And an intensity adjustment unit 103 that adjusts the pixel value after thinning the pixel.

  Thereby, it is possible to suppress the fluctuation of the line width after the image formation due to the image forming conditions, and it is possible to stabilize the line width after the thinning. Therefore, it is possible to reproduce the image-formed character or graphic with the expected line width.

[Other Embodiments]
The line width of a character or graphic may vary depending on whether the line constituting the character or graphic is a vertical line or a horizontal line.
In order to stabilize the line width after thinning regardless of whether it is a vertical line or a horizontal line, the intensity adjusting unit 103 determines whether the line width after thinning depends on whether it is a vertical line pixel or a horizontal line pixel. It is also possible to adjust the pixel value after thinning the contour pixel so that becomes an expected value.

FIG. 7A shows the measurement result of the line width when the vertical and horizontal test patterns having a line width of 2 pixels (42 μm at 1200 dpi) are formed with different development potentials. FIG. 7B shows the measurement results of the line widths of the vertical and horizontal lines when the same test pattern is formed with different laser powers.
7A and 7B, the solid line represents the horizontal line width, and the alternate long and short dash line represents the vertical line width.
As shown in FIGS. 7A and 7B, the line width tends to increase as the development potential and the laser power increase, but the vertical line tends to be larger than the horizontal line.

  As described above, the storage unit 107 stores the correspondence between the image forming conditions obtained by measurement in advance and the line widths of the vertical and horizontal lines. The intensity adjustment unit 103 obtains the estimated values of the vertical and horizontal line widths according to the image forming conditions from the correspondence stored in the storage unit 107, and uses the difference obtained by subtracting the estimated value from the expected value for the horizontal line and The adjustment value for the vertical line is calculated respectively.

For example, the intensity adjusting unit 103 obtains the estimated values W11 and W12 of the vertical and horizontal line widths corresponding to the setting value V1 of the development potential from the correspondence shown in FIG. When the width of one pixel is 21 μm, the intensity adjustment unit 103 uses the estimated values W11 and W12 to obtain adjustment values for vertical lines and horizontal lines as follows.
Adjustment value for vertical line (%) = 100 × {(Wt−W11) / 2} / 21
Adjustment value for horizontal line (%) = 100 × {(Wt−W12) / 2} / 21
Similarly, the estimated values W21 and W22 of the vertical and horizontal line widths corresponding to the set value E1 of the laser power are obtained from the correspondence shown in FIG. 7B, and the adjustment values for the vertical and horizontal lines are obtained. Ask for.

  The intensity adjustment unit 103 sets the contour pixel whose edge direction P is 2 or 3 as a vertical contour pixel, and adds each vertical line adjustment value to the pixel value after thinning the contour pixel. In addition, the intensity adjustment unit 103 sets the contour pixel whose edge direction P is 0 or 1 as the horizontal contour pixel, and adds each adjustment value for the horizontal line to the pixel value after thinning the contour pixel.

The intensity adjusting unit 103 can adjust the intensity of thinning in the same way even when the image forming condition is the type of paper.
In the case of the type of paper, the intensity adjusting unit 103 obtains a measurement value of the line width when the test pattern of the vertical line and the horizontal line having a predetermined line width is formed on each type of paper, and according to each type. Determine adjustment values for vertical and horizontal lines. The intensity adjustment unit 103 stores the determined adjustment values in the storage unit 107, reads out the adjustment values for vertical lines and horizontal lines according to the type of paper used for image formation from the storage unit 107, and generates vertical lines. Are added to the pixel values after the thinning of the contour pixels and the horizontal contour pixels.

FIG. 8 is a flowchart showing a processing procedure when the image processing apparatus 9 thins a character or a figure and the thinned outline pixel adjusts the thinning intensity according to the vertical outline pixel or the horizontal outline pixel. It is.
As shown in FIG. 8, the contour detection unit 101 determines the contour pixel of a character or graphic and the edge direction of the contour pixel (step S21).
Next, the thinning unit 102 reduces the pixel value of the contour pixel of the character or figure according to the edge direction determined by the contour detection unit 101, and thins the line (step S22).
The halftone processing unit 105 performs halftone processing on the thinned image data (step S23).

  The intensity adjusting unit 103 estimates the line widths of the vertical and horizontal lines according to the set value of the development potential (step S24). The intensity adjustment unit 103 determines an adjustment value for thinning of each of the vertical and horizontal lines from the difference between the estimated value of the vertical line and the horizontal line and the expected value (step S25).

  Similarly, the intensity adjusting unit 103 estimates the line widths of the vertical and horizontal lines according to the set value of the laser power (step S26). The intensity adjustment unit 103 determines an adjustment value for thinning of each vertical line and horizontal line from the difference between the estimated value and the expected value of each line width of the vertical line and horizontal line (step S27).

When the contour pixel determined by the contour detection unit 101 is a vertical contour pixel, the intensity adjustment unit 103 determines the pixel value after thinning the contour pixel according to the development potential and the laser power. The adjustment values for vertical lines are added to adjust the strength of thinning.
Further, when the contour pixel determined by the contour detection unit 101 is a horizontal contour pixel, the intensity adjustment unit 103 determines the pixel value after thinning the contour pixel according to the development potential and the laser power. The horizontal line adjustment values are added to adjust the thinning intensity (step S28).
The contone processing unit 104 performs contone processing on the image data adjusted by the intensity adjustment unit 103 and outputs the processed image data (step S29).

  If each pixel of the image data is a contour pixel determined by the contour detection unit 101, the output selection unit 106 outputs the image data output from the intensity adjustment unit 103. The output selection unit 106 outputs the image data output from the halftone processing unit 105 if it is a pixel other than the contour pixel determined by the contour detection unit 101 (step S30).

  The above-described processing procedure is an example in the case where the thinning intensity is adjusted according to the maximum density condition during image formation. When the image forming condition is a paper type, the thinning intensity can be adjusted by the same processing procedure except that an adjustment value corresponding to the paper type is acquired from the storage unit 107.

Fig.9 (a)-FIG.9 (c) have shown the processing result of the thinning mentioned above.
FIG. 9A shows the letter T and each pixel of the background. The pixel value of the character portion has a maximum value of 100%, and the background pixel value has a minimum value of 0%. Also, the arrow in FIG. 9A indicates the edge direction of the contour pixel determined by the contour detection unit 101.
When thinning is performed by the thinning unit 102, the pixel values of adjacent pixels in the background located in the direction opposite to the edge direction are merged with the contour pixel of the character, so that as shown in FIG. Is uniformly reduced.

Furthermore, when the negative adjustment value is added to the pixel value of the vertical outline pixel whose edge direction is the left-right direction (the arrow is → or ←) by the intensity adjustment unit 103, it is shown in FIG. 9C. As described above, the vertical outline pixels are more strongly thinned. On the other hand, when the positive adjustment value is added to the pixel value of the horizontal outline pixel whose edge direction is the vertical direction (arrow is ↓ or ↑) by the intensity adjusting unit 103, as shown in FIG. In addition, thinning of the horizontal outline pixels is alleviated.
The line width after image formation becomes thinner as the pixel value increases due to the adjustment value, and becomes thicker as the pixel value decreases, so that a character thinned with the thinning coefficient f is finally obtained.

  As described above, according to another embodiment, the image forming apparatus G analyzes the image data, determines the outline pixel of the character or figure and the edge direction of the outline pixel, and the outline The pixel value of a pixel is reduced according to the edge direction of the contour pixel, and a thinning unit 102 that thins a character or a figure, and a thin line depending on whether the contour pixel is a vertical line pixel or a horizontal line pixel And an intensity adjusting unit 103 that adjusts the pixel values after thinning of the vertical and horizontal outline pixels so that the line width after the conversion becomes an expected value.

  Thereby, it can suppress that line width fluctuates depending on whether it is a vertical line or a horizontal line, and the line width after thinning can be stabilized. Therefore, it is possible to reproduce the image-formed character or graphic with the expected line width.

The above-mentioned other embodiment is a preferred example of the present invention, and the present invention is not limited to this. Modifications can be made as appropriate without departing from the spirit of the present invention.
For example, the contour detection unit 101 can determine contour pixels by filtering image data using a Sobel filter, a Prewitt filter, or the like.
Further, although the intensity adjusting unit 103 determines whether the pixel is a vertical outline pixel or a horizontal outline pixel according to the edge direction, it can also be determined by pattern matching.

Further, the intensity adjusting unit 103 can adjust the intensity of thinning as a vertical outline pixel or a horizontal outline pixel even with respect to an outline pixel whose edge direction P is an oblique direction of 4 to 7. is there.
For example, the intensity adjustment unit 103 adjusts the thinning intensity by using the contour pixels whose edge direction P is 4 and 5 as vertical line contour pixels, and the contour pixels whose edge directions 6 and 7 are horizontal line contours. The intensity of thinning can be adjusted as a pixel.

  Also, the correspondence between the image forming conditions and the line width may vary. Therefore, the control unit 1 causes the image forming unit 10 to periodically form a test pattern, causes the scanner 7 to read the test pattern, measures the correspondence between the image forming conditions and the line width, and stores the test pattern in the storage unit 107. The correspondence relationship may be updated.

  Further, the processing procedure of the image processing device 9 shown in FIGS. 5 and 8 is programmed, the program is stored in the storage unit 2, the control unit 1 reads and executes the program, and the same processing as that of the image processing device 9 is performed. It can also be realized by software. As a computer-readable medium for the program, a non-volatile memory such as a ROM and a flash memory, and a portable recording medium such as a CD-ROM can be applied. A carrier wave is also used as a medium for providing program data via a communication line.

G Image forming apparatus 1 Control unit 2 Storage unit 6 Print controller 9 Image processing apparatus 101 Outline detection unit 102 Thinning unit 103 Strength adjustment unit 104 Contone processing unit 105 Halftone processing unit 106 Output selection unit 10 Image forming unit

Claims (5)

Analyzing the image data, the contour detection unit for determining the edge pixel of the contour pixel and the contour pixel of the character or figure,
A thinning unit that reduces the pixel value of the contour pixel in accordance with the edge direction of the contour pixel and thins the character or figure;
In accordance with image forming conditions, an intensity adjustment unit that adjusts the pixel value after thinning of the contour pixels so that the line width after thinning becomes an expected value;
An image forming apparatus comprising: Analyzing the image data, a contour detection unit that determines a contour pixel of a character or a figure and an edge direction of the contour pixel;
A thinning unit that reduces the pixel value of the contour pixel in accordance with the edge direction of the contour pixel and thins the character or figure;
Depending on the image forming condition and whether the contour pixel is a vertical or horizontal contour pixel, the vertical and horizontal contour pixels are thinned so that the line width after thinning becomes an expected value. An intensity adjustment unit for adjusting the pixel value of
An image forming apparatus comprising: The image forming condition is maximum density or paper type.
The image forming apparatus according to claim 1 or 2. Analyzing image data and determining a contour pixel of a character or a figure and an edge direction of the contour pixel;
A thinning step of reducing the pixel value of the contour pixel according to the edge direction of the contour pixel, and thinning the character or figure,
According to the image forming conditions, an intensity adjustment step of adjusting the pixel value after thinning of the contour pixels so that the line width after thinning becomes an expected value;
An image processing method including: Analyzing image data and determining a contour pixel of a character or figure and an edge direction of the contour pixel;
A thinning step of reducing the pixel value of the contour pixel according to the edge direction of the contour pixel, and thinning the character or figure,
Depending on the image forming condition and whether the contour pixel is a vertical or horizontal contour pixel, the vertical and horizontal contour pixels are thinned so that the line width after thinning becomes an expected value. An intensity adjustment step of adjusting the pixel value of
An image processing method including: