JP2006135395A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that noise is added so as to eliminate a level difference called banding appearing at the density converter of an image, however, roughness of the image is made conspicuous when increasing an addition level. <P>SOLUTION: An attribute is determined by referring to PDL data of the image for each pixel of image data. Image formation is executed by adding different noise to the image data corresponding to the attribute. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that performs color output.

Conventionally, when a gradation image is printed with an electrophotographic color printer, a step called banding is conspicuous in the density change portion, so noise is added to the entire image data, making the banding inconspicuous, and gradation output. A technique that makes it appear smooth has been used (see, for example, Patent Document 1).
JP 2000-134475 A

  However, the above color image forming apparatus has a demerit that the roughness of the image becomes conspicuous on the contrary, although the effect of eliminating the banding is increased if the added level of noise is increased.

In order to overcome the above problems, an image forming apparatus according to the present invention includes:
-Original image data generation means such as a PDL rasterizer,
Image area determination means for determining the original PDL object for each pixel,
・ Noise adding means to change the noise level according to the image area,
An image forming unit such as an electrophotographic color printer is provided, and the smoothness of gradation and the image with less roughness are made compatible by changing the noise addition level according to the image area.

  By the above processing, the noise to be added can be automatically changed according to the characteristics of the image data. It is possible to suppress the roughness of the image while smoothing the gradation, so that the output image quality can be improved.

  An image forming apparatus as described above.

(First embodiment)
The first embodiment of the present invention will be described below.

[System configuration]
FIG. 2 shows the system configuration of the first embodiment. Reference numeral 203 denotes a network composed of 100BaseT Ethernet (registered trademark), to which a personal computer (PC) 201 and a color copying machine 202 are connected. Other devices are also connected to the network 203, but are omitted. The color copying machine 202 functions as a postscript printer compatible with the network and can print a color image from the PC 201.

[Internal block]
FIG. 1 is an internal block diagram of the color copying machine 202 of the first embodiment.

  In FIG. 1, reference numeral 101 denotes a scanner, which optically reads a document, converts it into an electric signal, and generates RGB (Red, Green, Blue) digital data in which each pixel has 8-bit luminance information. The raster data has a resolution of 400 dpi in both the main scanning direction and the sub-scanning direction.

  Reference numeral 102 denotes image processing including input masking, log conversion from RGB to CMYK (Cyan Magenta, Yellow, blacK), output masking, and the like.

  A noise adding device 103 adds random noise data to 8-bit density data.

  A printer 104 forms a color image by electrophotography based on the received frame sequential CMYK data.

  A frame buffer 105 is a synchronous DRAM having a size of 139 MB. Raster image data fetched from the scanner is stored or written by the CPU.

  Reference numeral 106 denotes a CPU bus.

  A CPU 107 controls the color copying machine and uses Intel Pentium (registered trademark) III, 600 MHz.

  Reference numeral 108 denotes an I / O port connected to the CPU bus 106, which controls the scanner 101 and printer 104 and inputs sensor signals.

  109 is a ROM that contains software that runs when this system boots. It is connected to the CPU bus 106.

  110 is a work RAM, which is a 117 MB synchronous DRAM. In practice, the frame buffer 105 is combined with a 256 MB synchronous DRAM memory module. It is connected to the CPU bus 106.

  Reference numeral 111 denotes a SCSI controller. It is connected to the CPU bus 106.

  Reference numeral 112 denotes a 3.5 inch 9.1 GB hard disk drive connected to the SCSI controller 111.

  A network I / F controller 113 is connected to the CPU bus 106. It is connected to an external 10BaseT, 100BaseT, or 10Base5 Ethernet (registered trademark) network to exchange data.

  Reference numeral 114 denotes an operation unit of the color copying machine, which includes an LCD panel, a touch panel, and buttons.

[Frame buffer]
FIG. 3 shows a memory map of the frame buffer 105. The frame buffer 105 includes C, M, Y, and K planes 301, 302, 303, and 304 and a region code α (described later) plane 305. For C, M, Y, and K, data of 1 pixel = 8 bits is arranged as in 306. α is data of 1 pixel = 2 bits as in 307, and data of 4 pixels is packed in 1 byte.

[Region code α]
FIG. 4 shows the meaning of the area code α. For each pixel, if the pixel is described as a font object (that is, a character), α = 0 if there is no object in the original Postscript description (that is, white background), α = 1 if it is described as a raster image. If α = 2 is described as a vector object, it is recorded in the frame buffer 105 as α = 3. This is done at the same time as rasterizing the Postscript job. A noise level (described later) is determined in advance as shown in FIG.

[Noise adding device]
Details of the noise adding device 103 are shown in FIG. The input image data is an 8-bit data line that flows in MCYK frame order. A 2-bit area signal α is sent from the previous stage for each pixel. The random number generation device 503 generates a 3-bit wide random number based on the value of α in synchronization with the pixel synchronization clock signal VCLK. The range of the random number value is determined according to the noise level shown in FIG. For example, when α = 0, the noise level is 0, so the output of the random number is always 0, and when α = 2, the noise level is +/− 2, so a random number between −2 and +2 is output. The 8-bit width image data is delayed by the same amount as the random number generation by the buffer 501 and added to the random number by the ADDER 502. This ADDER 502 has a function of rounding to 0 and 255 when the result of addition becomes smaller than 0 or larger than 255, respectively.

[Copy operation]
The copy operation will be described with reference to FIG. When copying, the scanner 101 reads an original and generates RGB raster image data. The image processing unit 102 converts the image into one of CMYK, develops it in the printer 104 via the noise adding device 103, and outputs it to paper. This operation is repeated in the order of MCYK to form a color image.

  In the case of a copy operation, α input to the noise adding device is controlled so as to be always 0. That is, no noise is added to the copy image.

[Print operation]
The printing operation will be described with reference to FIG. When the user executes printing from the PC 201 to the color copier 202 using a printer driver, the color copier 202 receives a job described in postscript via the network I / F 113 and stores it in the work RAM 110. Then, the CPU 107 interprets the description of the postscript, generates a raster image, and stores it in the frame buffer 105. At this time, the area code α is generated and recorded in the frame buffer 105 as described above. The raster image is developed by the printer 104 via the noise adding device 103 and output to paper. This operation is repeated in the order of MCYK to form a color image.

(Second embodiment)
In the first embodiment, α is determined for each object on the PostScript. However, α may be changed depending on whether the image content is a homogeneous surface, or α may be changed depending on the density of the image. By doing so, it is possible to lower the noise level on a homogeneous surface where roughness is more noticeable due to the addition of noise, or to lower the noise level in a high density region where banding itself is not noticeable.

1 is a block diagram illustrating an internal configuration of a color copying machine according to a first embodiment. It is a system configuration figure of the 1st example. It is a memory map of the frame buffer of a 1st Example. It is a table | surface of the area | region code (alpha) of 1st Example. It is a block diagram of the noise addition apparatus of 1st Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Scanner 102 Image processing part 103 Noise addition part 104 Printer 105 Frame buffer 106 CPU bus 107 CPU
108 I / O port 109 ROM
110 RAM
111 SCSI I / F
112 Hard disk drive 113 Network I / F
114 Operation Unit 201 Personal Computer 202 Color Copier 203 LAN
301 Frame buffer for cyan plane 302 Frame buffer for magenta plane 303 Frame buffer for yellow plane 304 Frame buffer for black plane 305 Frame buffer for α plane 306 1 byte of CMYK frame buffer 307 1 byte of α frame buffer 501 Buffer gate 502 Adder 503 Random number generation circuit

Claims (9)

An image forming apparatus including the following means and outputting gradation smoothly.
Original image data generation means: generates original image data.
Image area determination means: determines the type of image area for each pixel.
Noise addition means: Adds noise whose level is changed according to the type of image area determined by the image area determination means to the original image data.
Image forming means: forms an image of the raster image data finally obtained by the above processing. The image forming apparatus according to claim 1.
An image forming apparatus characterized in that the original image data generating means has PDL processing means for forming a raster image from PDL (page description language). The image forming apparatus according to claim 2.
An image forming apparatus, wherein the image area determining unit determines the type of the image area based on the type of the PDL object. The image forming apparatus according to claim 3.
An image forming apparatus, wherein the noise adding means adds noise at a weak level to a raster image object and at a strong level to a vector image object. The image forming apparatus according to claim 1.
An image forming apparatus characterized in that the original image data generating means has PDL processing means for forming a raster image from PDL (page description language). The image forming apparatus according to claim 1.
An image forming apparatus characterized in that the original image data generating means has document reading means. The image forming apparatus according to claim 1.
The image area determining means determines an image area having a uniform density and an image area not having the same density;
An image forming apparatus, wherein the noise adding means adds a weak level of noise to an image area having a uniform density. The image forming apparatus according to claim 1.
The image area determination means determines the image area according to the density,
An image forming apparatus characterized in that the noise adding means changes the level of noise added according to the density. The image forming apparatus according to claim 1.
An image forming apparatus, wherein the image forming means forms a color image composed of a plurality of element colors.

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