JP2000125123A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a color image forming device where dispersion as a result of separation of each process is prevented by providing a different separation means for compression data and noncompression data of different quality. SOLUTION: Received data are fed to a companding section 2 and also to a Log transform section 4. A 1st version is generated using noncompression data not passing through the companding section 2 and a 2nd and succeeding versions are generated using companded data. The Log transform section 4 conducts table transformation to transform a signal characteristic in a reflectance space into that in a density space. A filter section 5 consists of a smoothing filter and applies smoothing filter processing to the data when a pattern separation discrimination signal indicates a pattern. A color correction section 6 replaces part of a CMY signal with a signal K. A UCR section 7 calculates C', M', Y' signals to drive a printer. A gray scale processing section 8 applies dither processing to an area of data whose pattern is discriminated and gives the resulting data to an image output device 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus equipped with an image data compression function and reproducing a color image in a frame-sequential manner such as a one-drum type color copying machine. The present invention relates to an image forming apparatus provided with an image area separating device for reproducing with high image quality.

[0002]

2. Description of the Related Art In a conventional color copying machine having a single photosensitive drum, Y (yellow), Y (yellow),
Data of four colors of M (magenta), C (cyan), and K (black) are created, and four color planes are sequentially created and superimposed to reproduce a full-color image. B (blue), G (green), R
After the gray balance of the (red) color separation signal is adjusted, the signal is converted into a color material signal YMC. Then, black plate (K) generation and under color removal (UCR) are performed, moiré and halftone dots are removed and edge emphasis is performed in the region separation type filter unit, and after gamma correction, modulation is performed using gradation processed data. The charged photoreceptor is exposed to the laser light to form images of each color.

In an image forming apparatus having no memory for one page, four scans have to be performed, and each time the area is separated. However, the results of the four segmentation operations of Y, M, C, and K are not always the same due to vibration and noise. In this case, there is a problem in that a problem in image quality such as interruption of black characters appears. JP 5
According to the technology described in Japanese Patent Application Publication No. -145751, there is a memory for storing only one page of the area separation result obtained in the first edition, so that the separation result is the same in the printing of the fourth edition, and the above-mentioned problem is eliminated. I have. In an image forming apparatus having a page memory for one page, image data is stored in the page memory at the same time as printing of the first edition, and printing is performed with data read from the page memory for the second and subsequent editions. By having a page memory in place of the memory for storing the area separation results, the area separation results are the same for all versions, and the above-mentioned problem is eliminated. By the way, in an image forming apparatus having a page memory, rotation and editing of an image can be performed. In addition, since only one scan is required for one document, there are advantages in that power and noise can be suppressed, and the printing speed can be increased.

[0004]

However, the above-mentioned prior art (Japanese Patent Laid-Open No. 5-157551) has a disadvantage that a memory for storing the separation result is specially required, which leads to an increase in cost. Moreover, since this system does not have a page memory in the first place, the above-mentioned advantage does not exist. On the other hand, an image forming apparatus having a page memory has a problem that the memory capacity for one page is very large and the cost is high. Resolution 600 dpi, gradation 24 bits / pixel, paper size A3, 2
The capacity is as much as 56 MBytes. To reduce this capacity, a data compression technique may be applied. However, if the data read from the page memory is not the same as when printing the first edition, the separation result will not be the same for all editions.

Therefore, a first object of the present invention is to provide different separating means for each of different quality data (for example, uncompressed data and compressed data), so that there is no need to have a memory for holding the separation result. Another object of the present invention is to provide an image forming apparatus capable of preventing a deviation of the separation result from the first plate to the fourth plate. A second object of the present invention is to use different parameters (thresholds) as separation means for data of different qualities so that each data can be separated without having a memory for holding the separation result. Another object of the present invention is to provide an image forming apparatus capable of preventing a deviation of the separation result from the first plate to the fourth plate. A third object of the present invention is to provide an image forming apparatus that can prevent black character deterioration by setting a first plate, which is generated as uncompressed data, to a black plate.

[0006] A fourth object of the present invention is to provide, as a separating means,
It is an object of the present invention to provide an image forming apparatus capable of separating a picture area and maintaining the image quality of the picture area. The fifth of the present invention
It is an object of the present invention to provide an image forming apparatus which can determine a pattern separation using a feature in uncompressed data. A sixth object of the present invention is to provide an image forming apparatus capable of determining a pattern separation utilizing characteristics of compressed data.

[0007]

According to the first aspect of the present invention, reading means for digitally reading an original, and image output means for digitally outputting image data read by the reading means in a frame sequential method. Generating a signal for forming a first plate based on the first image area separating means from a plurality of image area separating means having different characteristic amounts and an uncompressed read signal from the reading means; Storage means for compressing and storing the signal, when generating a signal for imaging the second and subsequent editions, a first image area separation and a first image area separation from a signal obtained by restoring the signal stored in the storage means. Achieves the first object by generating signals to be imaged based on different image area separating means.

According to a second aspect of the present invention, there is provided a reading means for digitally reading an original, an image output means for digitally outputting image data read by the reading means in a frame sequential manner, and a threshold processing. An image area separating means for determining an area of an image, and a signal for forming an image of the first plate based on the image area separating means based on a first threshold value is generated from the uncompressed read signal by the reading means. Storage means for compressing and storing the signal, wherein when generating a signal for imaging the second and subsequent editions, a signal different from the first threshold value is obtained from a signal obtained by restoring the signal stored in the storage means. The second object is achieved by generating a signal for forming an image based on an image area separating unit based on a threshold value.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the image of the first plate is a black plate, thereby achieving the third object. According to a fourth aspect of the present invention, in the first aspect of the present invention, the fourth object is achieved by determining a picture area by a plurality of image area separating means.

According to a fifth aspect of the present invention, in the fourth aspect of the invention, one of the image area separating means for judging a picture is:
By determining the picture area from the presence or absence of halftone dots,
The fifth object is achieved. In the invention according to claim 6,
In the invention according to claim 5, one of the image area separating means for determining a picture achieves the sixth object by determining a picture area from the presence or absence of a white background.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. FIG.
FIG. 2 is a processing block diagram of the image processing apparatus according to the embodiment of the present invention. The image processing apparatus includes an image input device 1 such as a scanner, a compression / expansion unit 2 for entropy encoding data, a page memory 3 for storing compressed data, and a Log for converting a linear reflectance signal to a density linear signal. A conversion unit 4, a filter unit 5 composed of a smoothing filter, a color correction unit 6 for matching colors, a UCR unit 7 for performing a process of subtracting the K signal from each color material signal, and a halftone using a dither for a picture. It comprises a gradation processing unit 8 for expressing, a picture separating unit 9 for separating a picture from a document, and an image output device 10 such as a printer.

First, the outline of the example shown in FIG. 1 will be described. The image input device 1 such as a color scanner uses a CCD (photoelectric conversion element) or the like, and according to the response, a multi-valued digital signal (here, a reflectance linear 600 dpi
i8 bit signal: RGB of original document white → 255, black → 0)
Is output. The compression / decompression unit 2 first linearly converts the input B, G, and R image data into color space signals Y, I, and Q of luminance and chrominance. The conversion formula is shown below as an example.

[0013]

## EQU1 ## Y = 0.30R + 0.59G + 0.11B I = 0.74 (RY) -0.27 (BY) Q = 0.48 (RY) +0.41 (BY)

By the conversion to the color space, the statistical power of the image can be concentrated on the luminance signal Y, and the entropy can be reduced. Next, the Y, I, and Q signals are each subjected to subhand conversion. The simplest conversion formula is shown below as an example.

[0015]

S (n) = | (x (2n) + x (2n + 1)) / 2 | D (n) = x (2n) -x (2n + 1)

FIG. 2 is a diagram showing an example of subhand conversion. First, a low-pass filter S in the horizontal direction of the original image
(N), a high-pass filter D (n) is applied, and the same processing is performed in the vertical direction.
L), vertical high frequency (LH), diagonal high frequency (HH), low frequency (L
L) Four frequency band signals are generated. If the sub-hand conversion is performed recursively on the low-frequency coefficients where power is concentrated, entropy can be further reduced. Finally, the generated coefficients are quantized and stored in the page memory. The transform coefficient is quantized to a fixed number of bits for each block.
For example, for a 2 × 2 block of input 8 bits / pixel, LL = 8 bits, HL = LH = 9 bits, HH
= 10 bits conversion coefficient (total 36 bits) to 8 bits
Quantize to Since fixed length compression is performed in block units, address calculation in image rotation and editing processing becomes easy, and these can be processed at high speed.

If the distribution of the number of bits is changed according to the image area, more effective quantization can be performed. For example, in a block in which the absolute value of the high-frequency coefficient exceeds a predetermined value, the bit allocation of the high-frequency coefficient is increased for the low-frequency component, and in the other blocks, the bit allocation of the low-frequency coefficient is increased for the high-frequency coefficient. . When decompressing compressed data, inverse subhand conversion is performed using each quantization coefficient to obtain Y ′, I ′, and Q ′ signals, and inversely converted to B ′, G ′, and R ′. The sub-hand transform and the BGR⇔YIQ transform are lossless transforms, but the present compression method is an irreversible transform in the process of quantizing coefficients. It is reversible without quantization, but the input 32 bits / block is 36 bits / blo
It is not compressed because it is converted to ck.

Further, in this case, 32 bits / block is compressed to 8 bits / block. For example, if this is compressed to 6 bits / block, the compression ratio increases, but the quantization error increases and the image quality deteriorates greatly. In general, there is a conflicting relationship between the compression ratio and the image quality. The input data is sent to the compression / decompression unit 2 and also to the Log conversion unit 4 at the same time. In the first edition, the data is generated as uncompressed data that does not pass through the compression / decompression unit 2, and in the second and subsequent editions, data is generated as compressed / expanded data.

Next, as a pre-process for performing color correction at a later stage,
The Log converter 4 performs a table conversion for converting the characteristics of the signal from the reflectance space to the density space. Here, the output signal indicates the amount of ink. FIG.
When a picture separation determination signal to be described later is a picture, a smoothing filter process is performed. The color correction unit 6 is a circuit for removing a turbid component of a color separation filter and a turbid component of ink in a scanner, and is generally a masking method, a memory map method (interpolation method), or the like. Here, the former masking method will be described. The conversion is performed, for example, in the following linear format.

[0020]

C = k11 × c + k12 × m + k13 × y + k14 M = k21 × c + k22 × m + k23 × y + k24 Y = k31 × c + k32 × m + k33 × y + k34

Here, k11 to k34 are constants, which are determined based on experiments. Further, in the color correction unit 6, the C
A part of the MY signal is replaced with K (black). UCR
The unit 7 calculates C ', M', and Y 'signals for driving the color printer according to the following equation.

[0022]

C ′ = C−K M ′ = M−K Y ′ = Y−K

The gradation processing section 8 performs dither processing on the area in which the picture pattern is determined, and
Send data to 0. Next, the picture separating section 9 will be described in detail. The picture separation unit 9 has two separation methods, that is, when uncompressed data of the first edition is input and when compressed data of the second edition or later is input. First, the separation method for uncompressed data for the first edition is determined by the presence or absence of a halftone dot. In this example, as a method of detecting a halftone dot, for example, a dissertation “Image Area Separation Method of Mixed Image of Text / Pattern (Dot and Photo)” (IEICE Transactions Vol.
75-D2No. 1pp. 39-47 1992 1
Month) described in “4.1 Halftone dot area detection” method. This method focuses on the point that the density change in the halftone dot area is significantly different from that in the character amount area, detects the peak pixel, detects the halftone dot area, corrects the halftone dot area, and separates the halftone dot area. is there.

In the detection of the peak pixel, for example, in a block of 3 × 3 pixels, the density level L of the central pixel is higher or lower than that of all the surrounding pixels, and is diagonally interposed between L and the central pixel. When the density levels a and b of the existing pairs of pixels satisfy | 2 × Lab−> TH (fixed threshold value) for all four pairs, the center pixel is set as the peak pixel. In the detection of the halftone dot region, for example, if four or more blocks including a peak pixel are present in four blocks in units of 4 × 4 pixels, the target block is set as a halftone dot candidate region, and the other blocks are non-halftone dot regions. The area is determined. After determining the halftone / non-halftone candidate area, if four or more of the nine blocks around the target block are halftone candidate areas, the target block is set to a halftone area; It is a non-dot area. As a result, the block determined to be a halftone dot area is defined as a picture area. Here, what is important is that the separation result is switched in block units. Here, the mask of the separation determination process is moved by four pixels for the next determination process. FIG. 4 shows this state.

Next, the separation method for the compressed data for the second and subsequent editions is determined based on the presence or absence of a white background. In this example, it is determined whether or not the target block is a white background block by the following three-stage processing procedure. That is, in the first step, max (c, m, y) of the target pixel is obtained, and when this value is smaller than a predetermined threshold, the target pixel is set as a white pixel. In the second step, the white pixels are counted in the target block (4 pixels × 4 pixels), and when the counted value is larger than a predetermined threshold, the target block is set as a white background block candidate. In the third step, if at least one white background block candidate is found among the five blocks as shown in FIG. 5, the target block is set as a white background block. This processing is also performed in block units, and the mask of the separation determination processing is moved by four pixels for the next determination processing. In this way, a block that is not determined as a white background block is set as a picture area.

Next, a second embodiment will be described. The configuration of the device is the same as that of the first embodiment. The picture separating section 9 which is a feature of this embodiment will be described. Here, the separating means for uncompressed data and the separating means for compressed data are selectively used only by changing the parameters. As the separating means used here, the same "4.1 dot area detection" method as that used in the first embodiment is used. In this method, a peak pixel is detected and a halftone dot area is determined. By changing a threshold for determining a peak pixel, separation of uncompressed data and compressed data is supported. In the compressed data, the peak value of the halftone dot tends to decrease due to the quantization of the DC component and the like. Therefore,

[0027]

Thl: threshold value for uncompressed data> th2: threshold value for compressed data

By setting two thresholds to be used and selectively using them, picture separation is performed.

Next, a third embodiment will be described. In the first embodiment, the first edition uses uncompressed data and the second and later editions use compressed data, but the K edition is a version that generates black characters, and is more uncompressed than data degraded by compression. Better image quality can be obtained by using the above data.
In addition, since the data for the CMY plane for the second edition can be compressed except for the fine image quality such as black characters concentrated on the K plane, the compression efficiency can be improved. The data processing procedure is the same as in the first embodiment.

[0030]

According to the first aspect of the present invention, an image area separating means is provided for each of data of different qualities (for example, uncompressed data and compressed data), so that a memory for holding a separation result is provided. At least, it is possible to prevent the deviation of the separation result from the first edition to the fourth edition.

According to the second aspect of the present invention, for data of different qualities (for example, uncompressed data and compressed data), each data can be separated only by changing a parameter (threshold) as image area separating means. In this case, it is possible to prevent the deviation of the separation results from the first edition to the fourth edition without having a memory for holding the separation results.

According to the third aspect of the present invention, it is possible to prevent black character deterioration by setting the first version generated as uncompressed data to a black version. According to the fourth aspect of the present invention, as the image area separating means, it is possible to separate the picture area and maintain the picture quality of the picture area.

According to the fifth aspect of the present invention, it is possible to determine the pattern separation utilizing the characteristics of the uncompressed data. According to the sixth aspect of the present invention, it is possible to determine the pattern separation using the feature in the compressed data.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration according to a first embodiment.

FIG. 2 is a block diagram illustrating subband conversion of a compression / expansion unit.

FIG. 3 is a diagram showing a smoothing filter.

FIG. 4 is a diagram illustrating a state in which a separation process is performed in block units.

FIG. 5 is a diagram illustrating determination of a white background block.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image input device 2 compression / decompression unit 3 page memory 4 Log conversion unit 5 filter unit 6 color correction unit 7 UCR unit 8 gradation processing unit 9 picture separation unit 10 image output device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C087 AA09 AA15 AA16 BA03 BC03 BD33 BD36 BD40 5C077 MP02 MP06 MP08 PP27 PP32 PP33 PP38 PP39 PP44 PQ08 PQ22 RR16 RR21 TT03 TT06 5C079 HB01 HB03 LA01 LA03 LA03 LA03

Claims (6)

[Claims] A reading means for digitally reading an original; an image output means for digitally outputting image data read by the reading means in a frame sequential manner; and a plurality of image area separating means having different characteristic amounts. And a storage unit for generating a signal for forming an image of the first plate based on the first image area separating unit from an uncompressed read signal by the reading unit, and compressing and storing the read signal. When generating a signal for imaging the second and subsequent editions, an image is formed based on an image area separating means different from the first image area separating means from a signal obtained by restoring the signal stored in the storage means. A color image forming apparatus for generating a signal. 2. A reading means for digitally reading an original, an image output means for digitally outputting image data read by the reading means in a frame sequential manner, and an image area is determined based on threshold processing. An image area separating means, and a signal for forming an image of the first plate based on the image area separating means based on a first threshold is generated from the uncompressed read signal by the reading means, and the read signal is compressed and stored. When generating a signal for imaging the second and subsequent editions, an image area separating unit using a threshold different from the first threshold from a signal obtained by restoring the signal stored in the storage unit. A color image forming apparatus for generating a signal for forming an image based on the image. 3. The color image forming apparatus according to claim 1, wherein the image formation of the first plate is a black plate. 4. A color image forming apparatus according to claim 1, wherein the picture area is determined by a plurality of image area separating means. 5. An image area separating means for determining a picture,
5. The color image forming apparatus according to claim 4, wherein a picture area is determined based on the presence or absence of a halftone dot. 6. An image area separating means for judging a picture,
5. The color image forming apparatus according to claim 4, wherein the pattern area is determined based on the presence or absence of a white background.