JPH0691607B2 - Image processing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image processing method for reproducing a halftone image by dispersing error data generated during image processing in peripheral pixels.

[Description of conventional technology]

Conventionally, many laser beam printers (LBP), ink jet printers, etc., use a binary recording method of "whether to apply or not" a recording dot. In order to perform a copying process of an image having a halftone density such as a photograph or a halftone dot original document, a process for artificially reproducing the halftone of read halftone image data is performed by an image processing circuit. .

As one of such pseudo halftone processing methods, a so-called "dither method" is widely used at present.
There is.

The dither method has an advantage that the pseudo halftone expression can be performed at low cost because the hardware configuration is simple. However, this method also has the following drawbacks.

When the original is a halftone image such as a print, a periodic striped pattern (moire) occurs in the copied image, and the image deteriorates.

If the original contains line drawings, characters, etc., the line reproducibility is poor and the image deteriorates.

For the drawback of, the smoothing process (spatial filtering process) is applied to the read halftone image data.
There is a method such as edge enhancement processing for the drawback of No. 1, but in any case, it is difficult to obtain an image with good reproducibility for all kinds of images such as photographs, halftone images, line drawings, and characters. . Further, because of such processing, the circuit scale becomes large and complicated, and the original advantage of the dither method is lost.

From this background, there is a method called "error diffusion method" as a method of pseudo halftone processing that has been attracting attention in recent years.

The error diffusion method is a method that is characterized in that the density error during binarization is diffused to surrounding pixels so that the density can be saved. As a reference, RW Floyd and L. Steinberg “An A
daptive Algorithm for Spatial Gray Scale′SID 75 D
There is an igest.

There is no problem when this error diffusion method is applied to a copying apparatus for copying an image of the entire surface of an original by the scanning method shown in FIG. 1-b, but the scanning method shown in FIG. 1-a. Therefore, when it is applied to a copying apparatus that copies an image of the entire surface of a document, the following problems occur.

In FIG. 1-a, the image of the area of the image is sequentially read in the order shown, and the processing by the error diffusion method is sequentially performed. At this time, when the processing of the area is finished and the processing of the next area is started, the error in processing the area is lost. That is, since there is no carryover error of the area required when the binarization of the first and subsequent lines of the area is performed, the area cannot be correctly binarized.
Regions become discontinuous in processing, and streaks occur on the boundary.

Similarly, when binarizing the 255th and 256th pixels of each line of the area, the error information of the 1st and 2nd pixels of each line of the area is required, and the error information is insufficient (the boundary between the areas and the area). In (), since the correct binarization is not performed, the consistency deteriorates and streaks occur on the boundary.

The cause of the streak at the boundary of the processing area will be described in more detail with reference to FIG.

As a diffusion matrix for the error diffusion method, the matrix shown in FIG.
Consider the case where a × 5 diffusion matrix is used (the numbers represent examples of error distribution ratios).

In Figure 2-b, the number of pixels on each main scan line is 256.
It is assumed that a pixel is used and the second line in the sub-scanning direction of the main scanning 255th pixel in the area is described as a (255,2).

First, attention is focused on the a (255,1) pixel as the pixel of interest to be binarized. The error generated when binarizing a (255,1) is b (1,1), b (1,2), b (1,2), as is clear from the diffusion matrix in FIG. 2-a. 3) Will be added to the pixel.

Further, focusing on the a (256,1) pixel, the errors generated at the a (256,1) are b (1,1), b (1,2), b (1,3), b
(2,1), b (2,2), b (2,3) pixels. Similarly, the error generated at the 255th and 256th pixels of each line of the area is added to each pixel of the 1st and 2nd pixels of each line of the area.

Therefore, there is no problem when the scanning method of FIG. 1-b is used, but when the scanning method of FIG. 1-a is used, the error that occurs when binarizing the first and second pixels of each line of the area But,
It is not added as a necessary error when binarizing the 255th and 256th pixels of each area, and the binarization of each 255th and 256th pixel of each area cannot be performed correctly. In addition, since the error generated at the 255th and 256th pixels of each line of the area needs to be added to the 1st and 2nd pixels of each line of the area, the error information of the area is held when the processing is performed in the area. Unless this is done, the binarization of the first and second pixels of each line in the area will not be performed correctly. As a result, streaks occur at the area and the boundary between the areas.

[Object of the Invention]

The present invention eliminates the above-mentioned drawbacks of the prior art, and divides an image into a plurality of areas, and reproduces a halftone image by distributing error data generated during image processing to peripheral pixels for each area. It is an object of the present invention to provide an image processing method capable of preventing the occurrence of streaks in the joining of areas when performing the above.

[Explanation of Examples]

First, the principle for solving the above problem will be described with reference to FIG.

Considering the shape of the diffusion matrix as shown in FIG. 2-a, as described in the description of the prior art, each line in the area shown in FIG. It is necessary for binarization of the 255th and 256th pixels, and without this error information, the binarization of the 255th and 256th pixels of each line of the area cannot be performed correctly. Therefore, each line of the area 255,
It is understood that in order to correctly perform the binarization of the 256th pixel, the shape of the diffusion matrix (FIG. 3-a) may be changed so that the error generated in the area is not added to the area.

In the example of the form of the diffusion matrix shown in FIG. 3-a, the error is not distributed to the pixels in the direction opposite to the main scanning direction when viewed from the target pixel. Although a 4 × 4 diffusion matrix is used here, any shape may be used as long as the diffusion matrix has a shape that does not distribute an error to pixels in the direction opposite to the main scanning direction when viewed from the target pixel.

By making the shape of the diffusion matrix as shown in FIG. 3-a, as shown in FIG.
The error generated at the 1st and 2nd pixels is not diffused to the attention area, and the binarization of 255th and 256th pixels of each line of the attention area is correctly performed. Further, when binarizing the first and second pixels of each line in the rear area, it is only necessary to consider the error carried over from the target area to the rear area, and it is better than when the diffusion matrix shown in FIG. 2-a is used. Also, the processing circuit is simplified, and the "streaking" generated at the boundary between regions can be improved more than when the diffusion matrix shown in FIG. 2-a is used.

Next, a more detailed description will be given based on specific examples to which the present invention is applied.

(Outline Description) FIG. 4 shows an outline view of a digital color copying machine to which the present invention is applied.

The whole can be divided into two parts.

The upper part of FIG. 4 shows a color image scanner unit 1 (hereinafter referred to as “scanner unit 1”) that reads a document image and outputs digital color image data, and various digital color image data that are built in the scanner unit 1. In addition to the image processing described above, the controller unit 2 has a processing function such as an interface with an external device.

The scanner unit 1 has a built-in mechanism for reading a large-sized sheet document in addition to reading a three-dimensional object or sheet document placed downward under the document retainer 11.

Further, the operation unit 10 is connected to the controller unit 2,
It is for inputting various information as a copying machine. The controller 2 instructs the scanner unit 1 and the printer unit 3 on the basis of the input information.

Further, when it is necessary to perform complicated edit processing, a digitizer or the like is attached in place of the document pressing member 11 and connected to the controller unit 2 to enable high-level processing.

The lower part of FIG. 4 is a printer unit 3 for recording the color digital image signal output from the Conton roller unit 2 on recording paper. In this embodiment, the printer section 3 is a full-color ink jet printer using a recording head of the ink jet recording system described in Japanese Patent Laid-Open No. 54-59936.

The two parts of the above description are separable and can be installed at remote locations by extending the connecting cable.

(Printer Section) FIG. 5 is a cross-sectional view of the digital color copying machine of FIG. 4 seen from the side.

First, the exposure lamp 14, lens 15, image sensor 16
(In this embodiment, a CCD capable of reading a line image in full color) is used to display an original image placed on the original platen glass 17, a projected image by a projector, or a sheet original image by the sheet feeding mechanism 12. read. The read image is subjected to various kinds of image processing by the scanner unit 1 and the controller unit 2, and then recorded on the recording paper by the printer unit 3.

In FIG. 5, the recording paper is a small-sized standard size (in the present embodiment, A4 to A3 size) sheet cassette 20 for storing cut paper, and a large size (in this embodiment, A2 to A1 size).
It is supplied from a roller paper 29 for recording.

Further, as for paper feeding, by inserting the recording paper one by one from the manual feeding port 22 in FIG. 4 along the paper feeding unit cover 21, it is possible to feed paper from the outside of the apparatus (= manual feeding port feeding).

The pick-up roller 24 is a roller for feeding the cut sheets one by one from the sheet feeding cassette 20, and the fed cut sheets are conveyed to the first sheet feeding roller 26 by the cut sheet feeding roller 25. It

The roll paper 29 is sent out by the roll paper feed roller 30,
It is cut to a standard length by a cutter 31, and the first paper feed roller 26
Be transported to.

Similarly, the recording paper input from the manual feed port 22 is conveyed to the first paper feed roller 26 by the manual feed roller 32.

Pick-up roller 24, cut paper feed roller 25, roll paper feed roller 30, paper feed first roller 26, manual feed roller
Reference numeral 32 is driven by a paper feed motor (not shown) (in this embodiment, a DC servo motor is used), and on / off control can be performed at any time by an electromagnetic clutch attached to each roller.

When the printing operation is started by an instruction from the controller unit 2, the recording paper sheet selected and fed from any one of the above-described paper feed paths is conveyed to the first paper feed roller 26. In order to remove the skew of the recording paper, after forming a predetermined amount of paper loop, the first paper feed roller 26 is turned on to convey the recording paper to the second paper feed roller 27.

Between the paper feed first roller 26 and the paper feed second roller 27, the recording paper is slackened by a predetermined amount in order to perform an accurate paper feed operation between the paper feed roller 28 and the paper feed second roller 27. To make. The buffer amount detection sensor 33 is a sensor for detecting the buffer amount. By constantly creating the buffer during the paper conveyance, it is possible to reduce the load applied to the paper feed roller 28 and the second paper feed second roller 27, especially when the large-sized recording paper is conveyed, and the accurate paper feed operation is possible. Become.

When printing with the recording head 37, the scanning carriage 34 composed of the recording head 37, etc. is mounted on the carriage rail.
A reciprocating scan is performed on the top 36 by the scan motor 35. In the forward scan, an image is printed on the recording paper, and in the backward scan, the paper feed roller 28 feeds the recording paper by a predetermined amount. At this time, while the drive system is being detected by the buffer amount detection sensor 33 by the paper feeding motor, control is performed so that the predetermined buffer amount is always obtained.

The printed recording paper is ejected to the paper ejection tray 23 to complete the printing operation.

Next, a detailed description around the scanning carriage 34 will be given with reference to FIG.

In FIG. 6, a paper feed motor 40 is a drive source for intermittently feeding the recording paper, and drives the paper feed second roller 27 via the paper feed roller 28 and the paper feed second roller clutch 43.

The scanning motor 35 is a drive source for scanning the scanning carriage 34 in the directions of arrows A and B via the scanning belt 42. In this embodiment, pulse motors are used as the paper feed motor 40 and the scanning motor 35 because accurate paper feed control is required.

When the recording paper reaches the second paper feed roller 27, the second paper feed roller / clutch 43 and the paper feed motor 40 are turned on to convey the recording paper to the paper feed roller 28 on the platen 39.

The recording paper is detected by a paper detection sensor 44 provided on the platen, and the sensor information is used for position control, jam detection, and the like.

When the recording paper reaches the paper feed roller 28, the second paper feed roller / clutch 43 and the paper feed motor 40 are turned off, and the suction operation is performed from the inside of the platen 39 by a suction motor (not shown) to move the recording paper onto the platen 39. Make them adhere closely.

Prior to the image recording operation on the recording paper, the scanning carriage 34 is moved to the position of the home position sensor 41, then forward scanning is performed in the direction of arrow A, and cyan C, magenta M, Image recording is performed by ejecting yellow Y and black K inks from the recording head 37. When the image recording for a predetermined length is completed, the scanning carriage 34 is stopped, and conversely, the backward scanning is started in the direction of arrow B and the scanning carriage 34 is returned to the position of the home position sensor 41. During the backward scan, the paper feed by the length recorded by the print head 37 is performed in the direction of arrow C by driving the paper feed roller 28 by the paper feed motor 40.

In this embodiment, the recording head 37 is the above-described ink jet type ink jet nozzle, and four nozzles each having 256 nozzles assembled are used.

When the scanning carriage 34 stops at the position detected by the home position sensor 41, the recovery operation of the recording head 37 is performed. This is a process for performing a stable recording operation, and in order to prevent unevenness at the start of ejection caused by a change in the viscosity of the ink remaining in the nozzles of the recording head 37, the paper feeding time, the device This is a process of performing a pressurizing operation on the recording head 37, an idle ejection operation of ink, and the like under pre-programmed conditions such as an internal temperature and an ejection time.

By repeating the operation described above, image recording is performed on the entire surface of the recording paper.

(Scanner portion) Next, the operation of the scanner portion 1 will be described with reference to FIGS. 7 and 8.

FIG. 7 is a diagram for explaining a mechanical mechanism inside the scanner unit 1.

The CCD unit 18 is a unit composed of a CCD 16, a lens 15, etc., and a main scanning motor 50 fixed on the rail 5,
A drive system in the main scanning direction composed of a pulley 51, a pulley 52, and a wire 53 moves on the rail 54 to read an image on the platen glass 17 in the main scanning direction. The shading plate 55 and the home position sensor 56 are used for position control when the CCD unit 18 is moved to the home position for main scanning in the correction area 68 in the figure.

The rail 54 is mounted on the rails 65 and 69, and the sub-scanning motor 6
0, pulleys 67, 68, 71, 76, shafts 72, 73, wires 66, 70 are driven by a drive system in the sub-scanning direction. Light shield 5
7.The home position sensors 58 and 59 are books that read documents such as books and three-dimensional objects placed on the platen glass 17.
It is used for position control when moving the rail 54 to the home position of each sub-scan in the sheet mode in which the sheet is read in the mode.

Sheet feed motor 61, sheet feed rollers 74 and 75, pulley
Reference numerals 62 and 64 and a wire 63 are a mechanism for feeding a sheet document. This mechanism is a mechanism that is provided on the platen glass 17 and that feeds a sheet document placed face down by the sheet feed rollers 74 and 75 by a predetermined amount.

FIG. 8 is an explanatory diagram of the reading operation in the book mode and the sheet mode.

In the book mode, move the CCD unit 18 to the illustrated book mode home position (book mode HP) in the correction area 68 in FIG. 8, and place the document placed on the platen glass 17 from there. Start reading the entire surface.

Prior to scanning the original, processing such as shading correction, black level correction, and color correction is performed in the correction area 68. afterwards,
The main scanning motor 50 starts scanning in the main scanning direction in the direction of the arrow shown. When the reading operation of the area shown by is completed, the main scanning motor 50 is rotated in the reverse direction and the sub scanning motor 60 is driven, and the correction area 68 of the area is moved in the sub scanning direction. Then, similar to the main scanning of the area (1), processing such as shading correction, black level correction, and color correction is performed as necessary, and the reading operation of the area (2) is performed.

By repeating the above scanning, the reading operation of the entire area of ~ is performed, and after the reading operation of the area of ~ is completed, the CCD unit 18 is returned to the book mode home position again.

In the present embodiment, since the document table glass 17 can read a document of maximum A2 size, in actuality, it is necessary to scan a larger number of times, but in the present description, it is simplified to make the operation easy to understand. .

In the sheet mode, the CCD unit 18 is moved to the sheet mode home position (sheet mode HP) shown in the figure, and the area of the sheet original sheet feeding motor 61
Repeatedly reading while performing intermittent operation to read the entire sheet original.

Prior to scanning the original, processing such as shading correction, black level correction, and color correction is performed in the correction area 68, and then the main scanning motor 50 starts scanning in the main scanning direction in the direction of the arrow shown. When the reading operation of the forward path of the area is completed, the main scanning motor 50 is rotated in the reverse direction, and the sheet feeding motor 61 is driven during the scanning of the forward path to move the sheet document by a predetermined amount in the sub scanning direction. Subsequently, the same operation is repeated to read the entire surface of the sheet original.

Assuming that the above-described reading operation is the same-size reading operation, the area that can be read by the CCD unit 18 is the fifth area.
As shown in the figure, it is actually a large area. This is because the digital color copying machine of this embodiment has a variable magnification function for enlargement and reduction. That is, since the recording area of the recording head 37 is fixed at 256 bits at a time as described above, for example, when performing a reduction operation of 50%,
This is because the image information of a 512-bit area which is at least doubled is required.

Further, the present scanning section 1 can be overlapped and read over a plurality of scanning areas.

(Description of Overall Function Block) Next, the function block of the digital color copying machine of this embodiment will be described with reference to FIG.

The control units 102, 111 and 121 are control circuits for controlling the scanner unit 1, the controller unit 2 and the printer unit 3, respectively, and are composed of a micro computer, a program ROM, a data memory, a communication circuit and the like. Control unit 102-111
And the control units 111 to 121 are connected by a communication line, and a so-called master / slave control mode in which the control units 102 and 121 operate according to an instruction from the control unit 111 is adopted.

When the control section 111 operates as a color copying machine,
Control operation is performed according to input instructions from the operation unit 10 and the digitizer 114.

The operation unit 10 uses, for example, a liquid crystal as a display unit, and is provided with a touch panel made of transparent electrodes on its surface so that selection instructions such as designation regarding color and designation of editing operation can be performed. It is an operation unit. Also, keys related to the operation, for example, a key for instructing the start of the copy operation (= start key), a key for instructing the stop of the copy operation (= stop key), and a key for returning the operation mode to the standard state (= reset key). Keys that are frequently used such as are installed independently.

The digitizer 114 is for inputting position information indicating a processing area for trimming, masking processing, color conversion, etc., and is connected as an option when complicated editing processing is required.

Further, the control unit 111 is, for example, IEEE-488, so-called GP-IB.
It also controls the control circuit (= I / F control unit 112) of general-purpose parallel interface such as interface, and performs input / output of image data between external devices and remote control by the external device via this interface. I am able to do things.

Further, the control unit 111 also controls the multi-level synthesis unit 106, the image processing unit 107, the binarization processing unit 108, the binary synthesis unit 109, and the buffer memory 110 that perform various types of processing relating to the image.

The control unit 102 controls the mechanical drive unit 105 that controls the drive of the mechanism of the scanner unit 1 described above, the exposure control unit 103 that controls the exposure of the lamp when reading a reflective original, and the halogen lamp when using the projector. The exposure control unit 104 that controls the exposure of 90 is controlled. Further, the control unit 102 also controls the analog signal processing unit 100 and the input image processing unit 101 that perform various types of processing related to images.

The control unit 121 controls the mechanical drive of the printer unit 3 described above, the mechanical drive unit 105 for absorbing the time variation of the mechanical operation of the printer unit 3, and the delay correction due to the arrangement of the recording heads 117 to 120 on the mechanism. The synchronous delay memory 115 for performing the control is controlled.

Next, the image processing block of FIG. 9 will be described in detail along with the flow of images.

The image formed on the CCD 16 is converted into an analog electric signal by the CCD 16. The converted image information is serially processed in the order of red → green → blue → analog signal processing unit 100.
Entered in.

The analog signal processing unit 100 performs sample-and-hold, dark level correction, dynamic range control, etc. for each color of red, green, and blue, and then performs analog-to-digital conversion (A / D conversion), and serial serial conversion. It is converted into a digital image signal of a value (8 bit length for each color in this embodiment) and output to the input image processing unit 101.

In the input image processing unit 101, correction processing necessary for the reading system such as shading correction, color correction, and γ correction is similarly performed with the serial multivalued digital image signal.

The multi-value synthesizing unit 106 of the controller unit 2 selects and synthesizes the serial multi-value digital image signal sent from the scanner unit 1 and the serial multi-value digital image signal sent via the parallel I / F. It is a circuit block that performs processing. The selectively combined image data is sent to the image processing unit 107 as it is as a serial multi-valued digital image signal.

The image processing unit 107 is a circuit that performs edge enhancement, black extraction, UCR, masking processing for color correction of recording ink used in the recording heads 117 to 120, and the like. The serial multi-value digital image signal output is input to the binarization processing unit 108 and the buffer memory 110, respectively.

The binarization processing unit 108 is a circuit for binarizing a serial multilevel digital image signal to which the error diffusion method is applied.
Here, the serial multi-valued digital image signal is converted into a four-color binary parallel image signal. 4 to the binary synthesis unit 109
Image data of three colors is sent to the color / buffer memory 110.

The binary synthesizing unit 109 selects and synthesizes the three-color binary parallel image signal sent from the buffer memory 110 and the four-color binary parallel image signal sent from the binarization processing unit 108. It is a circuit for converting a binary parallel image signal of four colors.

The buffer memory 110 is a buffer memory for inputting / outputting a multivalued image and a binary image via a parallel I / F.

The synchronous delay memory 115 of the printer unit 3 is a circuit for absorbing the time variation of the mechanical operation of the printer unit 3 and performing mechanical and delay correction of the recording heads 117-120. It also generates the timing required for driving.

The head driver 116 is an analog drive circuit for driving the recording heads 117-120.
A signal that can directly drive is generated internally.

The recording heads 117 to 120 eject inks of cyan C, magenta M, yellow Y, and black K, respectively, and record an image on recording paper.

(Example of Timing Signal) FIG. 10 is an explanatory diagram of the timing of an image between the circuit blocks described in FIG.

The signal BVE is 1 in the main scanning reading operation described in FIG.
It is a signal indicating the image effective section for each scan. Signal BVE
The image is output on the full screen by outputting multiple times.

The signal VE is a signal indicating the effective section of the image for each line read by the CCD 16. Only the signal VE when the signal BVE is valid is valid.

The signal VCK is a sending clock signal of the image data VD. The signal BVE and the signal VE also change in synchronization with this signal VCK.

The signal HS is a signal used when the valid and invalid sections are discontinuously repeated while the signal VE outputs one line, and is an unnecessary signal when the signal VE is continuously valid while the signal VE outputs one line. Is. This is a signal indicating the start of image output for one line.

(Specific Circuit Configuration Example of Image Processing Unit 107) Next, a specific circuit configuration example of the image processing unit 107 will be further described with reference to FIG.

The color-sequential three-color multi-valued image information (cyan C, magenta M, and yellow Y) sent from the multi-valued composition unit 106 is converted into a specific color designated by the digitizer 114 or the like by the color conversion circuit 201. It is a circuit for electrically converting to another color. By passing through this circuit, it is possible to convert a specific color of the original document (for example, a background color in a design image) into an arbitrary color.

Serial / parallel signal conversion circuit (SP conversion circuit) 20
Reference numeral 3 denotes a circuit for separating color-sequential three-color multi-valued image information for each color for color processing in the masking circuit 204 in the next stage.

The masking circuit 204 is a circuit for correcting the input color information and the color information in consideration of color reproducibility in the printer unit. Specifically, it is a circuit that performs arithmetic processing as shown in the following mathematical formulas.

YMC: Input data Y'M'C ': Output data a _{11 to} a ₃₃ : Correction coefficient The black extraction circuit 202 is for extracting the black component (black K) from the multi-valued image information of three colors in sequence. Circuit. Color component data having the lowest density value among cyan C, magenta M, and yellow Y is calculated and extracted as a black component.

A background removal circuit (UCR circuit) 205 calculates the black K component extracted by the black extraction circuit 202 and each of the cyan C, magenta M, and yellow Y components, and performs processing for improving color reproducibility. By passing through this circuit, the multi-valued image information of three colors in sequence (cyan C, magenta M, yellow Y) becomes four colors in sequence (cyan C, magenta M, yellow Y, black K).

The background removal circuit (UCR circuit) 205 may perform gamma correction and offset processing of image data values as necessary.

The edge emphasizing circuit 206 is a circuit that extracts an edge component for each color and performs addition and subtraction on the original image data. It is inserted in order to improve the reproducibility of thin lines and to reproduce images clearly. For example, the edge component is extracted by 3 × 3 arithmetic matrix processing as shown in the following equation.

The block processing circuit 207 is a circuit for reducing a peculiar striped pattern generated in an image, especially in a highlight portion when the error diffusion method is applied.

The image data processed by the block processing circuit 207 is binarized by the error diffusion method in the binarization processing unit 108.

The block processing circuit 207 is a circuit for eliminating the striped striped pattern generated in the highlight portion near the portion where the density changes abruptly. For example, the image is made into a block like a 4 × 4 matrix, and whether or not the corresponding block is the highlight part is detected by a predetermined algorithm. When the corresponding block is the highlight part, the density of pixels in the block is concentrated on a specific pixel to form a halftone dot to prevent the printing dots from being concentrated and the generated pattern becomes a striped pattern. Prevent.

A specific circuit configuration example of the block processing circuit 207 will be described with reference to FIG.

The maximum value detection circuit 210 and the minimum value detection circuit 211 are circuits for detecting the maximum density value Dmax and the minimum density value Dmin, respectively, in the pixels pixelated as a 4 × 4 matrix.

The total sum calculation circuit 212 is a circuit that similarly calculates the total sum Dsum of the density values of the pixels that are blocked.

Based on the maximum density value Dmax, the minimum density value Dmin, and the total sum Dsum,
The determination circuit 213 performs determination processing under the following conditions.

Dsum <Dconst ₁ (= constant) Dmax−Dmin <Dconst ₂ (= constant) When both conditions are satisfied, the halftone dot processing circuit 215 performs pseudo halftone dot processing on the pixels in the block. If the condition is not satisfied, the image data is passed through.

The delay circuit 214 is a line buffer that delays the pixels while the above determination processing is performed. For example, when the delay circuit 214 is a block like a 4 × 4 matrix, it only needs to have a buffer amount of 4 lines.

In the halftone dot processing circuit 215, when the above conditions are satisfied, the following processing is performed on the pixels in the block. In this case, the block is a 4 × 4 matrix.

In order to retain all the density data in the block, the density of # pixel is reduced to 1 / n, and the density is added to * pixel by that amount. Since the density data is stored, the merits of the pixel diffusion method are not lost by this processing.

Concentration distribution, processing block also increase the number of judgment steps,
You may make it detailed.

Also, like the blocks A and B, the blocks may be changed for each color so that the dots do not overlap for each color.

In other words, the probability of dots being printed is high for the pixels on which density is applied, so the concentration concentration can be changed by changing the processing block to A or B, and the probability that each color dot will be applied to the same position. Can be lowered.

By carrying out such a block process, it is possible to disperse the printing dots and prevent the occurrence of a striped striped pattern which occurs in the highlight portion near the portion where the density change is abrupt.

Next, a specific circuit configuration example of the binarization processing unit 108
This will be described with reference to FIGS. a and 13-b.

Here, the image data is a two-dimensional array, and the i-th image data in the main scanning direction and the j-th image data in the sub-scanning direction are represented by Di, j.

FIG. 13-b is an error distribution matrix diagram, showing arbitrary image data D _{i, j} (pixel of interest) input to the binarization processing unit 108.
In contrast, the error data that occurs when binarization is performed at a certain ratio
It is the figure which showed the mode of the error at the time of dividing into 15 pieces of error data, and distributing to a peripheral pixel. _{I and j} of each error data are
It is shown that the error is generated in the image data D _{i, j} .

That is, in this binarization processing, the matrix shown in FIG. 13-b sequentially accumulates errors by one pixel in the main scanning direction, and accumulates the errors. The result of addition with the image data input as the pixel of interest is binarized.

FIG. 13-a is a circuit diagram showing the circuit configuration of the binarization processing unit of this embodiment.

In FIG. 13-a, 301 to 312 are delay sections consisting of four-stage flip-flops, which process color-sequential (cyan, magenta, yellow, black) image data for each color. The delay unit delays data by 4 clocks in order to delay by 1 pixel.

313 to 327 are adders. The adders from 313 to 326 are
In order to perform the error calculation in the error diffusion matrix, the error data and the error data are added and subtracted, and the adder 327 performs the addition and subtraction of the error data which is the error calculation result in the error diffusion matrix and the input image data. ing.

328 and 330 are error line memories using, for example, a FiFo (Fast In-Fast Out) memory, which stores the error calculation result of each line and delays by one line.

Reference numeral 331 is an error distribution unit composed of a ROM (Read Only Memory). Reference numeral 332 is a comparator that compares the addition result of the error data and the image data with a set threshold value, and 333 is a gate circuit that performs gate processing on the output data.

Reference numeral 334 is a connection error memory for storing the error data of the connection part of the image.

Next, the operation of FIG. 13-a will be described.

The image data input to the binarization processing unit 108 is as follows.
The error data output from the delay unit 312 is added to the error data by the adder 327 and then input to the error distribution unit 331. Error distribution unit 3
In 31, the error data (a, b, c, d, calculated on the preset distribution ratio is calculated using the look-up table of ROM.
e, f, g) is output. The output of the adder 327 is the comparator 33
In step 2, it is compared with a preset threshold value and binary output of 1 or 0 is performed. The binarized output of the comparator 332 is input to the gate unit 333, and only the necessary pixels are output.

Here, the error data output from the error distribution unit 331 for the image data D _{i, j} is a _{i, j} , b _{i, j} , c _{i, j} , d _{i, j} e _{i, j} ,
If f _{i, j} , g _{i, j} , the error data g _{i, j} is delayed by four colors by the delay unit 301, and then the error data g _{i + 1 of} the same color generated in the pixel of the image data D _{i + 1, j , j} are added by the adder 313.

After that, after being similarly processed as 302, 314, 303, 315, the output of the adder 315 is input to the line memory unit 328. The stored error addition data is output again after being delayed by one line in the line memory unit 328. The read error addition data is input to the adder 316.

Thereafter, similarly, the error data generated in the other pixel data are sequentially added in 304, 317, 305, 318, 306, 319, and the error data ci ₊₃ , j ₊₁ generated in the input image data Di ₊₃ , j ₊₁ is added in the adder 319, and then the line is added. It is input to the memory unit 329. The error data output from the line memory unit 329 is input to the adder 320, and thereafter, similarly processed by 307, 321, 308, 322, 309, 323, the error data is added by the adder 323, and then input to the line memory unit 330.

The error data output from the line memory unit 330 is 324,3
After adding error data at 10,325,311 and 326, adder 3
At 27, it is added to the image data. Next, the addition result of the error data and the image data is input to the error distribution unit 331 and the comparator 332.

Taking the input image data D _{i, j} as an example, the process described above
When expressed by a formula, it becomes like the following formula.

DD _{i, j} = D _{i, j} + gi _-3 , j _-3 ＋ gi _-2 , j _-3 ＋ fi _-1 ,, j _-3 ＋ ei, j _-3 ＋ gi _-3 , j _-2 ＋ ei _-2 , j _-2 ＋ di _-1 , j _-2 + ci, j _-2 ＋ fi _-3 , j _-1 ＋ di _-2 , j _-1 ＋ bi _-1 ,, j _-1 ＋ ai, j _-1 ＋ ei _-3 , j ＋ ci _-2 , j ＋ ai _-1 , j DD: Data after calculation D: Image data i: Pixel number in line (by color) j: Line number Next, the circuit operation will be described using the timing chart of FIG. This figure shows a timing chart in the case of a single color for easy understanding of the operation. At the actual timing, the number of pixels is equal to the number of colors, that is, 4 colors = 4 times.

Image data of a plurality of lines can be obtained by one scan of the CCD unit 18 of the scanner unit 1 described above.

Now, in the case of processing the attention area of FIG. 3-b, in the first scan, sw1 is connected at the timing of control B shown in FIG. 14, and each line 257 in the rear area of FIG. 3-b is connected. Th, 258
The respective error data to be added to the th and 259th (corresponding to the first, second, and third in the rear area) image data are stored in the connection error memory unit 334 from the delay unit 312. These error data are read from the connection error memory 334 in synchronism with the first, second and third image data of the corresponding line of the plurality of lines obtained by the next scan. That is, sw2 is connected to the connection error memory 334 at the timing of control A shown in FIG. The read error data is sent to the adder 327 by sw2, added to the corresponding image data, and then sent to the error distribution unit 331 and the comparator 332 for error distribution and binarization processing.
257th, 258th and 259th in the rear area (corresponding to the 1st pixel, 2nd pixel and 3rd pixel in the area next to the rear area)
The error data to be added to the image data is stored in the connection error memory 334 via sw1 as in the first scan described above.

Thereafter, in accordance with the timing shown in FIG. 14, similarly, the error data in the connection portion is written to and read from the connection error memory 334.

As described above, by storing the error information at the joint portion, it is possible to obtain an image output completely free of joint lines as described above.

In this embodiment, the table distribution by the ROM is used for the error distribution unit 331, but it goes without saying that a RAM, a multiplier or the like may be used.

[Other possible embodiments]

FIG. 15 to FIG. 17 are diagrams showing examples of other image outputs that require image joining information when the error diffusion method is applied.

FIG. 15 is an example in which the magnification ratio is increased and the original image is divided into four and output on the roll paper 29 in the copying apparatus described above.

In this example, in addition to the part of the image connection described above, 1, 2, ...
A portion requiring new image joining information occurs in the portion indicated by the broken line in each output image of 3 and 4.

FIG. 16 shows a print paper from one original when cut paper is used in the above-mentioned copying apparatus or when cut paper is similarly used in a copying apparatus using a printer such as LBP. This is an example in which enlarged continuous shooting is performed on four images.

In this example, a portion requiring new image joining information occurs in the portion indicated by the broken line of each of the images 1, 2, 3, and 4 of the document. That is, in the print paper, all the places where the images come into contact are the places that require the image joining information.

FIG. 17 is an example showing a portion of image joining which occurs when images are combined in the copying apparatus described above.

This is an example in which an image area indicated by A and B is magnified and printed on a print paper as illustrated. In this case, if copying is performed in the order of A1, B1, A2, B2, an image connecting portion will occur at the boundary portion indicated by the broken line on the print paper. But,
In this example, unlike the above example, in order to copy like A1, B1, A2, B2, it is necessary to individually manage the image connection information at the boundary between A1 and A2 and the boundary between B1 and B2. is there.

15 to 17, it can be seen that in any of the examples, the error data of the joint portion of the image can be stored in the memory and used in the processing to solve the image joint problem when the error diffusion method is applied. .

[Explanation of effects]

As described above, according to the image processing method of the present invention, when an image is divided into a plurality of areas and image processing is performed for each area,
The error data distributed from the area preceding the area of interest to the area of interest is stored in the memory, the error data stored in the memory is used for image processing of the area of interest, and image processing is performed on the image data of the area of interest. Since the error data generated at this time is not distributed to the pixels of the previous area that have already undergone image processing, it is possible to prevent the occurrence of streaks in the connection between areas.

[Brief description of drawings]

FIG. 1-a and FIG. 1-b are diagrams showing an example of image processing for explaining a problem to be solved by the present invention. FIGS. 2-a and 2-b are views for explaining in detail the problems to be solved by the present invention. 3A and 3B are views for explaining the outline of the present invention. FIG. 4 is an outline drawing of a digital color copying machine to which the present invention is applied. FIG. 5 is a side sectional view of the digital color copying machine of FIG. FIG. 6 is a detailed explanatory view around the scanning carriage 34. FIG. 7 is a view for explaining a mechanical mechanism inside the scanner unit 1. FIG. 8 is an explanatory diagram of the reading operation in the book mode and the sheet mode. FIG. 9 is an explanatory diagram of a function block of a digital color copying machine to which the present invention is applied. FIG. 10 is a diagram showing an example of an image timing chart. FIG. 11 is a diagram showing an example of a specific circuit configuration block of the image processing unit 107. FIG. 12 is a diagram showing an example of a specific circuit configuration block of the block processing circuit 207. FIG. 13-a is a specific circuit configuration block diagram of the binarization processing unit 108. FIG. 13-b is a diagram showing an error diffusion matrix. FIG. 14 is a diagram showing an example of a specific timing chart of the binarization processing unit 108. FIG. 15, FIG. 16, and FIG. 17 are diagrams showing an example of image output that requires image connection information.

Claims (1)

[Claims] 1. An image processing method for reproducing a halftone image by dispersing error data generated during image processing to peripheral pixels, wherein an image is divided into a plurality of areas, and image processing is performed for each area. , The error data distributed from the area before the area of interest to the area of interest is stored in the memory, the error data stored in the memory is used for image processing of the area of interest, and image processing is performed on the image data of the area of interest. An image processing method, characterized in that error data generated at the time of performing the processing is not dispersed to pixels of the previous region which have already undergone image processing.