JP2009152766A - Image forming apparatus, image forming method and program for executing image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus capable of eliminating scattering of toner at an edge part of a linear image, or the like, and forming a sharp image. <P>SOLUTION: The average density of a prescribed area is calculated, the threshold of binarization is changed according to the calculated average density, pattern matching is performed using the changed threshold, and thinning processing is performed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, an image forming method, and a program for executing an image forming method having a function of performing image correction processing such as addition / deletion of pixels on a specific portion or region of a rasterized image. .

  Print data and image data sent from input devices such as copiers and printers such as host computers and scanners are developed into rasterized images, image processing is performed, print data is generated, and output (printing) devices and functions are used. Some apparatuses that print on media have a function of correcting generated print data in accordance with the characteristics of the output apparatus. For example, if data consisting of a single pixel (such as a line with a width of 1 pixel) is generated faithfully to the original image, it may not be printed properly on the media depending on the pixel reproduction capability of the output device. The image may be faded or faded. When such a thing is predicted in advance, an appropriate amount of pixels may be added to the print data in advance to provide a function of correcting the image so that the output image is printed with an appropriate density. In addition, when all pixel data included in a certain area has the maximum density, such as a solid-filled image, for example, in an electrophotographic printing apparatus, a lot of toner adheres to the painted area. It may be scattered outside the area to be placed. In order to prevent this, the applied amount of toner is reduced by thinning out part of the generated print data. As a result, the density is reduced as compared with the case of outputting the original print data, but it is possible to suppress the scattering of the toner due to the overload amount. For example, Patent Document 1 discloses a method of detecting an edge portion of an image, calculating an optimum density of the edge portion, and converting the density of the edge portion in order to reduce toner scattering.

However, in Patent Document 1, a large processing load is required for calculating the optimum density of the edge portion, which complicates the apparatus and increases the apparatus cost. In order to solve this, for example, in Patent Document 2, it is determined whether or not image data corresponding to a window area matches a determination pattern, and image processing for changing a predetermined position pixel value of the window area that matches the determination pattern Disclosed is a method for outputting image data having undergone the above.
JP 9-65142 A JP 2006-295624 A

  However, these conventional techniques target binary images, and the threshold value used for edge determination of a solid image region is fixed (eg, all pixels other than black pixels are regarded as white pixels). There was a problem that it was not subject to processing. On the other hand, in the case of a threshold value that considers all pixels other than white pixels to be black, there is a problem in that a low density area that is originally unnecessary to be processed is also a processing target, causing unnecessary image deterioration.

  In order to solve the above-described problem, the present invention includes means for determining a threshold value by making the threshold value for edge determination variable, determining the necessity level of toner application amount control based on the peripheral pixel density of the determination target pixel. It is characterized by.

  According to the present invention, it is possible to effectively control the toner application amount by a simple method using the same pattern matching process as that of the binary image in the printing result of the image data having the intermediate density level.

Example 1
Examples of the present invention will be described below.

  First, an explanation will be given of the original transported and discharged original surface by taking as an example the configuration of a copying machine including an image reading section and an image printing section as a general image reading / forming apparatus.

FIG. 3 is a block diagram showing the configuration of the entire copying machine. The image data read by the document reading unit 100 is sent to the data processing / control unit 102 via the input unit I / F 110. The sent data is processed on the RAM 109 while the CPU 108 starts up the data processing program stored in the program ROM 106 and uses the processing data stored in the data ROM 107. Image data during or after processing is stored in the internal storage area 103 via the storage I / F 114 as necessary. The processed image data is sent to the data transmitting / receiving unit 104 or the image output unit 105 via the output unit I / F 112. The data sent to the former is sent to another data processing device connected to the outside such as a host computer 116 existing on the network. The data sent to the latter is printed and output on a medium such as paper from a print engine provided in the copying machine. Also, print data may be received from an external host computer 116 via the data transmission / reception unit 104. (At this time, the copier operates as a printer.)
The operating environment for executing the series of print data and image data processing is set by the user from the environment setting unit (panel) 101. According to the setting contents, the operation setting of the data processing / analysis unit is performed via the setting unit I / F.

  The above is the configuration of a general copying / printing apparatus.

  Next, the difference between the processing according to the prior art and the processing according to the present invention will be described with reference to FIGS.

  FIG. 2 shows image replacement processing of a binary image according to the prior art. In the conventional processing, the user first confirms the print result, selects ON / OFF of the scattering reduction processing function such as S201 toner, and further selects a function level indicating how much pixel replacement is performed in S202. In other words, if the scattering of the print result is large, the level of thinning out pixels is set to reduce the toner amount and suppress the scattering. After ON / OFF / level selection, print data is sent to the image processing unit in S203. In step S204, the image processing unit analyzes the print data. In step S205, the multi-value image data is subjected to halftone processing and converted to a binary image. Thereafter, a thinning pattern is selected according to the level set in S206, and edge determination by pattern matching is performed on the binary image in S207. The image area determined to be an edge by a predetermined matching algorithm is replaced with the thinning pattern selected in S208, the replaced image is sent to the data printing unit in S209, the printing operation is performed in S210, and the process is terminated.

  If the rasterized image is binary as shown in (1) of FIG. 5 as a result of performing the image processing by the conventional processing, the boundary between the black pixel and the white pixel of the image shown in (2) of FIG. Therefore, the thinning pattern is applied as shown in (3) of FIG. 5, and the toner amount can be reduced to a level at which scattering does not occur.

  However, when the rasterized image is multivalued as shown in (1) of FIG. 6, the edge determination threshold is 100%, and in the case of an algorithm in which all pixels other than the full density black pixels are all white pixels, (2) of FIG. Since the boundary between the intermediate gray pixel and the white pixel of the image shown in FIG. 6 is not determined as an edge, the thinning pattern is not applied as shown in (3) of FIG. 6, and the toner amount cannot be lowered to a level at which scattering does not occur.

  Therefore, in the present invention, the image including the intermediate gray is processed by the algorithm shown in FIG.

  After performing S201 to S203 in FIG. 2, the print data is analyzed in S301 when the print data is received, and halftone processing from multivalue to multivalue is performed in S302. In step S303, a determination area having a certain size is determined for the halftone-processed image, and an average density value in the determination area including the target pixel for edge determination is calculated. At this time, as a calculation method, there is a method of dividing a value obtained by adding density values for pixels in the region by the number of pixels in the region. In step S304, an edge determination threshold value corresponding to the average density obtained in step S303 is selected. At this time, there is a method in which a threshold value lookup table defined in advance corresponding to the average density value is held in the image processing apparatus and the threshold value is selected by referring to the table. Further, this threshold has a feature that when the average density is high, the threshold is set low so that the edge determination is easy, and when the average density is high, the threshold is set high and the edge determination is difficult.

  Using the threshold value selected here, edge determination is performed in S305, a thinning pattern corresponding to the set value is selected in S306, pixel replacement processing is performed using the thinning pattern in S307, and image output processing is performed in S308. And proceed to S210.

  As a result of performing the processing according to the present invention, even when the rasterized image is multi-valued as shown in (1) of FIG. 7, the edge determination threshold varies depending on the average density of surrounding pixels including the target pixel for edge determination. Therefore, the boundary between the intermediate gray pixel and the white pixel in the image shown in (2) of FIG. 7 is easily determined as an edge if the peripheral pixel density is high. Therefore, the thinning pattern is applied as shown in (3) of FIG. 7, and the toner amount can be lowered to a level at which scattering does not occur.

(Example 2)
The present embodiment is characterized in that the user does not turn on / off the scattering suppression function or sets the level but makes a determination on the image processing apparatus side.

  In the first embodiment, the user sets the scattering processing function ON / OFF and the level in steps S201 to S203, but this processing is not performed in the present embodiment.

  Steps up to S305 in FIG. 3 are the same as those in the first embodiment. In S401, an appropriate amount thinning rate N% is acquired when the average density of the original image is 100% (equivalent to solid black). Since this information is determined depending on the image output device, it is data stored in advance in the image processing device as information on the corresponding image output device. Next, a thinning pattern corresponding to the appropriate amount thinning rate N calculated in S402 is generated. Here, it may be generated directly, or a thinning pattern corresponding to an appropriate thinning rate may be held in advance.

  Using the thinning pattern generated / acquired here, the process proceeds to S307 to perform pixel replacement processing.

It is a block diagram explaining the printing apparatus which implements this invention. It is a flowchart explaining the flow of the process in a prior art. It is a flowchart explaining the flow of the process concerning Example 1 of this invention. It is a flowchart explaining the flow of the process concerning Example 2 of this invention. It is a schematic diagram at the time of processing a binary image by a prior art. It is a schematic diagram at the time of processing a multi-value image by a prior art. It is a schematic diagram at the time of processing a multi-value image according to the present invention.

Claims (3)

In an electrophotographic image processing apparatus that performs a replacement process on a target pixel for the purpose of adjusting a toner loading amount of a filled image area using a pattern matching with edge detection as a determination target,
A means for comparing the density value (multivalue) of the target pixel with one threshold value and determining whether the target pixel is determined to be black or white in edge detection and replacement determination. A peripheral region including the target pixel is to be replaced. Means for calculating an average density of pixels in the area defined as an area. ・ A threshold determination means for setting a threshold low when the average density is high, and setting a threshold high when the average density is low. An image processing apparatus.   2. The image processing apparatus according to claim 1, further comprising means for holding a look-up table for associating the average density of the peripheral area with the threshold and selecting a threshold corresponding to the calculated average density. 2. The image processing apparatus according to claim 1, wherein a replacement pattern is selected by selecting a correlation between an average density in a fixed area and a toner application amount, and a thinning rate in a replacement target area corresponding to a target toner reduction amount from the average density. means.

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