JP2013120368A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in which: although there has conventionally been a toner saving method by using a masking pattern, an image masked by a uniform pattern causes interference with dithering, which results in occurrence of moire or texture that degrades image quality, and is likely to result in occurrence of pseudo contour in a natural image.SOLUTION: The occurrence of moire or texture is suppressed by masking pixels at the same cycle as the size of a base matrix that indicates the growth order of dithering. The occurrence of pseudo contour is suppressed by equally masking a dot of earlier growth order and a dot of later growth order.

Description

  The present invention relates to a printer device that saves toner used in an electrophotographic image output unit.

  As an image recording method used in an image forming apparatus such as a printer or a copying machine, an electrophotographic image is formed by forming a latent image on a photosensitive drum using a laser beam and developing it with a charged color material (hereinafter referred to as toner). The method is known.

  Conventionally, as a technique for saving toner in an electrophotographic system, the amount of toner consumption is reduced by performing a logical operation (AND) on an image immediately before output in an image output unit and a mask pattern, thereby reducing a drawing area. A reduction is being made. In general, uniform masking generates moiré and texture that interferes with dither and impairs image quality. Moreover, it is easy to generate a pseudo contour in a natural image.

  In order to solve such problems, a proposal has been made to achieve both maintenance of image quality and toner saving (Patent Document 1). According to this method, the toner is saved and the maximum gradation is maintained by switching the dither threshold for toner saving when toner is saved.

JP-A-9-123524

  With the method described above, it is necessary to prepare a dither threshold matrix for toner saving. When masking is performed at an arbitrary mask rate, a memory corresponding to the dither threshold matrix is required.

The present invention
Switch between a mode that reduces toner consumption and a mode that outputs normal image quality.
Determine the text area, photo area, drawing area from the image data,
Prepare a mode to reduce toner consumption for each area,
An image processing unit that sets a mode for suppressing the toner consumption for each region according to a result of the determination unit, and suppresses toner consumption;
The image processing means for suppressing toner consumption creates a mask pattern for equally masking fast growing pixels and slow growing pixels by dividing the growing order of dithers into integers in a base matrix indicating the growing order of dithers, An image processing apparatus characterized by taking a logical product with a dither threshold matrix.

  By the image processing means of the present invention, it is possible to suppress the interference between the mask pattern and the dither and to suppress the occurrence of moire in the binarized output image. In addition, the user can select from a plurality of mask ratios, and the user can determine the balance between the toner consumption and the image quality, which improves convenience. Moreover, generation | occurrence | production of the pseudo contour in a natural picture can be suppressed.

1 is a block diagram illustrating a schematic configuration of an image processing apparatus according to an embodiment of the present invention. It is an example of the dither base matrix in one Embodiment concerning this invention. It is a figure explaining the binarization process using the dither method as a general halftone process. It is an example of the table | surface used for mask pattern preparation in Embodiment 1 (the 1). It is an example of the table | surface used for mask pattern preparation in Embodiment 1 (the 2). 3 is an example of a mask pattern in the first embodiment.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

[Embodiment 1]
[Configuration of image forming apparatus]
FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus according to the present embodiment. The image processing apparatus according to the present embodiment includes an image reading unit 101, an image processing unit 102, a storage unit 103, a control unit 104, and an image output unit 105. The image processing apparatus according to the present embodiment can be connected to a server that manages image data, a PC that instructs printing, and the like via a network.

  The image reading unit 101 reads an image of a document and outputs image data.

  The image processing unit 102 converts print information including image data input from the image reading unit 101 or the outside into intermediate information (hereinafter referred to as an object) and stores it in an object buffer of the storage unit 103. At that time, image processing such as density correction is performed. Further, bitmap data is generated based on the object stored in the buffer and stored in the buffer of the storage unit 103. At that time, density adjustment processing, printer gamma correction processing, halftone processing by dithering, and the like are performed.

  The storage unit 103 is composed of a hard disk (HD) or the like, and is used as the above-described object buffer or the like. By accumulating image data on the object buffer, it is possible to sort pages and to accumulate a plurality of sorted originals and print out a plurality of copies.

  The control unit 104 includes a ROM, a RAM, a CPU, and the like. The ROM stores various control programs and image processing programs executed by the CPU. The RAM is used as a reference area or work area where the CPU stores data and various types of information. As the object buffer described above, not only the storage unit 103 but also a RAM in the control unit 104 can be used.

  The image output unit 105 forms a color image on a recording medium such as recording paper based on the image data stored in the buffer of the storage unit 103 and outputs the color image.

[Halftone processing]
The principle of image binarization by the dither method for a two-tone printer will be described below with reference to FIG. The input multi-valued image (for example, 8-bit gradation image) is divided into N × M (8 × 8 in the figure) blocks, and the gradation values of the pixels in the block are the same size as the N × M dither threshold matrix. If the pixel value is larger than the threshold, black is output, and white is output otherwise. By performing this for all pixels for each matrix size, the entire image can be binarized.

[Mask processing]
A toner saving method by mask processing in this embodiment will be described with reference to FIG.

  First, in step S401, the image processing unit 102 reads an object stored in the object buffer of the storage unit 103, and inputs a multi-value image.

  In step S <b> 402, the image processing unit 102 performs area determination for each pixel. By the determination process, a character area, a drawing area, and a photograph area are determined. The types to be identified are not limited to the above three types.

  In step S403, the control unit 104 determines whether to perform toner saving processing.

  In step S404, the control unit 104 performs mask processing for each region. The logical product of the mask pattern determined for each area and the dither threshold matrix corresponding to the area is taken as a dither threshold matrix for toner saving. The mask pattern setting method will be described later.

  In step S405, the image processing unit 102 performs dither processing on the multi-valued image to generate a halftone image.

[Set mask pattern]
A method for creating a mask pattern in the present invention will be described.

  FIG. 2 is an example of a dither base matrix showing the dither growth order. Although the actual threshold value is entered in the dither threshold value matrix including the gamma characteristic in the threshold value, the growth order is lit as shown in FIG. In this example, the number of gradations is 64.

  4A and 4B are tables in which the gradation number of the base matrix is divided into three equal parts. Numbers indicate growth order.

  Next, a portion to be uniformly masked is determined from the three divided portions. As an example, the mask rate is 50%. That is, 32 out of 64 gradations are masked. Reference numeral 402 shown in FIG. 4B is an example in which the mask is evenly allocated to the three parts. The part marked with “x” is the part to be masked.

  The mask rate can be arbitrarily determined, and the portion to be masked equally is determined from the equally divided portions according to the mask rate.

  FIG. 5 shows a mask pattern determined by the above method. The shaded part is the part to be masked.

101 Image Reading Unit 102 Image Processing Unit 103 Storage Unit

Claims (2)

A mode switching unit (S403) for switching between a mode for suppressing toner consumption and a mode for performing normal image quality output, and a unit (S402) for discriminating a character area, a photo area, and a drawing area from image data;
Prepare a mode (S404) to reduce toner consumption for each area,
An image processing unit that sets a mode for suppressing the toner consumption for each region according to a result of the determination unit, and suppresses toner consumption;
The image processing means for reducing the toner consumption amount divides the dither growth order into an integer number (401) in the base matrix (201) indicating the dither growth order,
Create a mask pattern (501) that equally masks fast-growing pixels and slow-growing pixels,
An image processing apparatus characterized by taking a logical product of the mask pattern and a dither threshold matrix. The image processing apparatus according to claim 1, wherein an arbitrary mask ratio is set by adjusting the number of masks with respect to the number of gradations of the base matrix of the dither in the growth order of the dither divided into integers.