JPS63309457A - Processing of image - Google Patents

Abstract

PURPOSE:To prevent a line on a border part between images from occurrence, by a method wherein after image memory over a plurality of divided mutual adjacent scanning regions are stored in memory, the image data stored in the memory are processed by an error diffusion method. CONSTITUTION:When a form of a diffusion matrix is to be considered, data of one scan content, for instance, data of a region (a) are stored in memory, and signal processing direction conversion of main scanning and subsidiary scanning is performed. That is, after a signal is converted by using the memory, binary processing of error diffusion or the like is performed, and reverse signal conversion is performed by using the memory again. By performing such a process as abovementioned, image data partially read can be treated as a sheet of continuous images, and a problem of an 'line' having been generated on the boundary between the regions abovementioned can be solved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Description of the Field to which the Invention Pertains] The present invention relates to an image processing method for devices that perform digital image processing, such as digital copying machines, image scanners, printers, and the like.

[Description of conventional technology]

Conventionally, laser beam printers (LBP) and ink printers
Many jet printers use a binary recording method of "printing or not" for recording dots.
In a copying device that applies this, in order to copy images with halftone density such as photographs and halftone originals, the halftone image data that has been read is used to reproduce the halftones in a pseudo manner using an image processing circuit. is being processed.

One of the methods of pseudo-halftone processing is the so-called "dither method," which is currently widely used.
There is.

This dither method has the advantage of being able to express the above-mentioned pseudo halftones at low cost because of its simple hardware configuration. However, this method also has the following drawbacks.

■ If the original is a halftone image such as a print, periodic striped patterns (moiré) occur in the copied image, degrading the image.

■ If the original contains line drawings, characters, etc., the reproducibility of the lines will be poor and the image will deteriorate.

To address the drawback of ■, smoothing processing (spatial filtering processing) is applied to the read halftone image data.
There are countermeasures against the drawback (2), such as edge enhancement processing, but in either case, it is impossible to obtain images with good reproducibility for all types of images such as photographs, halftone images, line drawings, and text. difficult.

Furthermore, the circuit scale is large due to such processing, and the original advantages of the complicated redizer method are lost.

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

The error diffusion method is a method that is characterized by diffusing the density error during binarization to surrounding pixels and preserving the density.
d L, Steinberg An Adaptiv.
e Algorithm for 5patial
Gray 5cale″SID 75 Dige
There is st.

There is no problem when this error diffusion method is applied to a copying machine that copies an image of the entire surface of a document using the scanning method shown in Figure 1-b. When this method is applied to a copying apparatus that copies an image of the entire surface of a document, the following problems arise.

In FIG. 1-a, the images of the area ``■'' and the area ``■'' are sequentially read in the order shown in the figure, and are sequentially processed by the error diffusion method. At this time, when the processing of the ■ area is finished and the process moves on to the next ■ area, the error in processing the ■ area will be lost.

In other words, since there is no carryover error of the ■ area, which is necessary when performing binarization from the first line of the ■ area, correct binarization of the ■ area cannot be performed, and the ■ area and the ■ area are It becomes discontinuous and a streak appears on the boundary.

Similarly, each line 255 in the ■ area. Also when performing binarization of the 256th pixel, each line l of the ■ area.

Error information for the second pixel is required, and correct binarization is not performed in areas where error information is insufficient (boundary between the ■ area and ■ area), resulting in poor consistency (and streaks appear on the boundary). It ends up.

The cause of the occurrence of streaks at the boundaries of the processing areas will be explained in more detail with reference to FIG.

3 shown in Figure 2-a as a diffusion matrix for the error diffusion method.
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 in each main scanning line is 25.
It is assumed that there are 6 pixels, and the second line in the sub-scanning direction of the 255th main-scanning pixel in the area ■ is described as a (255, 2).

First, a (255°1
) Focus on pixels. As is clear from the diffusion matrix in Figure 2-a, the errors that occurred during the binarization of a (255, 1) are b (1, 1), b (1, 2), b (1,
3) Will be added to the pixel.

Also, if we pay attention to a (256,1) pixel, a (2
The error generated at 56°l) is b(1,1), b(1,
2), b(1,3), b(2,1), b(2,2), b
(2,3) is added to the pixel. Thereafter, similarly, the error occurring at the 255th and 256th pixel of each line in the ■ area is added to each pixel of each line 1 and the 2nd pixel of the ■ area.

Therefore, there is no problem when using the scanning method shown in Figure t-b, but when using the scanning method shown in Figure 1-a, a problem occurs when binarizing the 1st and 2nd pixels of each line in the ■ area. The error is
■Each line of the area 255. It is not added as a necessary error when binarizing the 256th pixel, and each line 2 of the ■ area
55. Binarization of the 256th pixel cannot be performed correctly.

Also, the error that occurs at the 255° and 256th pixel of each line in the ■ area needs to be added to the 1.2 pixel of each line in the ■ area, so when processing is performed in the ■ area,
As long as the error information of the area is not retained, the binarization of the 1st and 2nd pixels of each line in the area (2) will not be performed correctly. As a result, streaks occur at the boundary between the ■ area and the ■ area.

[Purpose of the invention]

An object of the present invention is to provide an image processing method for solving the problems of the prior art described above in image processing using the error diffusion method or the minimum average error method, which is equivalent in principle.

〔Example〕

First, the principle for solving the above problem will be explained using FIG.

When considering the shape of the diffusion matrix as shown in FIG. 2-a, the problem described in the description of the prior art occurs.

Therefore, it is conceivable to store one scan's worth of data (for example, data in the ■ area) in a memory as shown in FIG. 3, and convert the signal processing direction between main scanning and sub-scanning.

In other words, after converting the signal shown in Figure 1-a to the signal shown in Figure 1-b using memory, binarization processing such as error diffusion is performed, and then the memory is used again to convert the signal into the signal shown in Figure 1-b. This is a method of performing signal conversion. (This main-scan/sub-scan conversion will be explained in detail below.) By performing the above processing, partially read image data can be treated as one continuous image, and the above It is possible to eliminate the problem of "streaks" that occur at the boundaries between regions.

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

(Explanation of External Shape) FIG. 4 shows an external 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 l (hereinafter abbreviated as scanner unit l) that reads the original image and outputs digital color image data, and a color image scanner unit l (hereinafter abbreviated as scanner unit l) that reads the original image and outputs digital color image data. The controller section 2 performs image processing and has processing functions such as interface with external devices.

The scanner unit l has a built-in mechanism for reading a three-dimensional object and a sheet original placed downward under the original presser 11, and also for reading a large-sized sheet original.

Further, the operation section 10 is connected to the controller section 2, and is used to input various information regarding the copying machine. The controller section 2 instructs the scanner section 11 and printer section 3 regarding operations according to the input information.

Further, when it is necessary to perform complicated editing processing, a digitizer or the like is attached in place of the document presser 11, and this is connected to the controller section 2, thereby making it possible to perform sophisticated processing.

The lower part of FIG. 4 is a printer section 3 for recording the color digital image signal output from the controller section 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 method described in Japanese Patent Laid-Open No. 54-59936.

The two parts described above can be separated, and can be installed at separate locations by extending the connecting cable.

(Printer Section) FIG. 5 is a sectional view of the digital color copying machine shown in FIG. 4 viewed from the side.

First, an exposure lamp 14, a lens 15, and an image sensor 16 (in this embodiment, a C0D capable of reading line images in full color) are used to scan the original platen glass 1.
A document image placed on the document sheet 7, an image projected by a projector, or a sheet document image by the sheet feeding mechanism 12 is read. The scanned image undergoes various image processing at the scanner section.
After that, the controller section 2 prints the image, and then the printer section 3 records it on recording paper.

In FIG. 5, recording paper is stored in a paper feed cassette 20 that stores cut paper of small standard sizes (A4 to A3 size in this example) and large size (A2 to A1 size in this example). It is supplied from a roll paper 29 for carrying out the process.

In addition, paper feeding from outside the apparatus (=manual paper feeding) is also possible by feeding recording paper one sheet at a time along the paper feeding unit cover 21 through the manual feeding port 22 shown in FIG.

The pick-up roller 24 is a roller for feeding cut sheets one by one from the paper feed cassette 20, and the fed cut sheets are conveyed to the 10th feed roller 26 by the cut paper feed roller 25. be done.

The roll paper 29 is sent out by a roll paper feed roller 30, cut into a standard length by a cutter 31, and then transferred to the paper feed number 10.
- It is conveyed to La 26.

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

Pick up roller 24, cut paper feed roller 25
, the roll paper feed roller 30, the 10th paper feed roller 26, and the manual feed roller 32 are connected to a paper feed motor (not shown in the drawings, D
It is driven by a C servo motor (using a C servo motor), and can be turned on and off at any time by electromagnetic clutches attached to each roller.

When the printing operation is started in accordance with an instruction from the controller section 2, recording paper selectively fed from one of the above-mentioned paper feeding paths is conveyed to the paper feeding path 26. In order to eliminate the skew of the recording paper, after creating a predetermined amount of paper loops, the 10th paper feeder 26 is turned on and the recording paper is conveyed to the 20th paper feeder 27.

Between the 10th paper feed roller 26 and the 20th paper feed roller 27, a predetermined amount of paper is applied to the recording paper in order to perform an accurate paper feeding operation between the paper feed roller 28 and the 20th paper feed roller 27. Create a buffer. The buffer amount detection sensor 33 is a sensor for detecting the buffer amount. By creating a buffer in the middle of paper transport, it is possible to reduce the load on the paper feed roller 28 and paper feed roller 27, especially when transporting large-sized recording paper, allowing accurate paper feeding operation. become.

When printing with the recording head 37, the recording head 3
A scanning carriage 34 consisting of 7 etc. is a carriage.
The rail 36 is scanned back and forth by the scanning motor 35. In the forward scan, an image is printed on the recording paper, and in the backward scan, the paper feed roller 28 performs an operation to feed the recording paper by a predetermined amount. At this time, while the drive system is detected by the buffer amount detection sensor 33 using the paper feed motor, control is performed so that the buffer amount is always a predetermined amount.

The printed recording paper is discharged to the paper discharge tray 23, and the printing operation is completed.

Next, the scanning carriage 3 and the invention will be described in detail using FIG.

In FIG. 6, a paper feed motor 40 is a drive source for intermittently feeding the recording paper, and a paper feed roller 28,
The 20th paper feeder 27 is driven via the 0-ra clutch 43.

The scanning motor 35 moves the scanning carriage 34 to the scanning belt 42.
This is a drive source for scanning in the directions of arrows A and H through the arrows. In this embodiment, since accurate paper feeding control is required, pulse motors are used for the paper feeding motor 40 and the scanning motor 35.

When the recording paper reaches paper feed number 20-27, paper feed number 20
-La clutch 43 and paper feed motor 40 are turned on, and the recording paper is conveyed over the platen 39 to the paper feed roller 28.

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

When the recording paper reaches the paper feed roller 28, the paper feed number 20-
The clutch 43 and the paper feed motor 40 are turned off, and a suction operation (not shown) is performed from inside the platen 39 to bring the recording paper into close contact with the platen 39.

Prior to the image recording operation on recording paper, the scanning carriage 34 is moved to the position of the home position sensor 41,
Next, forward scanning is performed in the direction of arrow A, and cyan, C1, magenta, M1, yellow, and black inks are ejected from the recording head 37 from predetermined positions to record an image. After recording the image for a predetermined length, the scanning carriage 34 is stopped, and reverse scanning is started in the direction of arrow B to return the scanning carriage 34 to the position of the home position sensor 41.

During the backward scan, the paper is fed by the length recorded by the recording head 37 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 an ink jet nozzle of the above-mentioned ink jet type, and uses four ink jet nozzles each having 256 nozzles assembled together.

Scanning carriage 34 is home position sensor 41
When it stops at the position detected by , the recording head 37 performs a recovery operation. This is a process for stable printing operation, and in order to prevent unevenness at the start of ejection caused by changes in the viscosity of the ink remaining in the nozzles of the print head 37, paper feed time, device The recording head 3 is adjusted according to pre-programmed conditions such as internal temperature and ejection time.
This is a process in which pressurizing operation to 7, idle ejection operation of ink, etc.

By repeating the operations described above, an image is recorded on the entire surface of the recording paper.

(Scanner Section) Next, the operation of the scanner section l will be explained using FIGS. 7 and 8.

FIG. 7 is a diagram for explaining the mechanical mechanism inside the scanner section l.

The CCD unit 18 is a unit composed of a CCD 16, a lens 15, etc., and includes a main scanning motor 50 fixed on a rail 54, a pulley 511, a pulley 52, and a wire 53.
It moves on the rail 54 by a drive system in the main scanning direction consisting of the following, and reads the image on the document platen glass 17 in the main scanning direction. The light shielding plate 55 and the home position sensor 56 are used for position control when moving the CCD unit 18 to the main scanning home position in the correction area 68 in the figure.

The rail 54 rests on rails 65 and 69, and is equipped with a sub-scanning motor 60, pulleys 67, 68, 71, 76, and shafts 72 and 69.
73, and is moved by a drive system in the sub-scanning direction consisting of wires 66 and 70. The light shielding plate 57 and the home position sensors 58 and 59 are used for sub-scanning in the book mode in which the document table reads a document such as a book or three-dimensional object placed on the lath 17, and in the sheet mode in which the sheet is read. It is used for position control when moving the rail 54 to its home position.

Sheet feed motor 61, sheet feed rollers 74 and 75,
The pulleys 62 and 64 and the wire 63 are mechanisms for feeding the sheet original. This mechanism is located on the document table glass 17, and transports the sheet document placed face down to the sheet feed roller 7.
This is a mechanism for feeding a predetermined amount at a time of 4.75.

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

In the book mode, the CCD unit 18 is moved to the book mode home position (book mode HP) shown in the correction area 68 in FIG. 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. Thereafter, scanning in the main scanning direction is started by the main scanning motor 50 in the direction of the illustrated arrow. When the reading operation of the area indicated by (2) is completed, the main scanning motor 50 is reversed and the sub-scanning motor 60 is driven to move the area (2) to the correction area 68 in the sub-scanning direction. Subsequently, similarly to the main scanning of the area (2), processing such as shading correction, black level correction, color correction, etc. is performed as necessary, and the reading operation of the area (2) is performed.

By repeating the above scanning, the entire areas ① to ② are read, and after the reading operation in the area ② is completed, the CCD unit 18 is returned to the book mode home position.

In this embodiment, the document platen glass 17 can read a maximum A2 size document, so in reality it must be scanned more times, but in this explanation, the operation is simplified to make it easier to understand. .

In the seat mode, the COD unit 18 is set to the seat mode home position (seat mode H) shown in the figure.
P), and repeatedly reads the sheet document in the area (3) while operating the sheet feed motor 61 intermittently, thereby reading the entire sheet document.

Prior to scanning the document, processing such as shading correction, black level correction, and color correction is performed in the correction area 68, and then scanning in the main scanning direction is started by the main scanning motor 50 in the direction of the arrow shown in the figure. When the forward scanning operation of the area (2) is completed, the main scanning motor 50 is reversed, and during this backward scanning, the sheet feed motor 61 is driven to move the sheet original by a predetermined amount in the sub-scanning direction. Subsequently, the same operation is repeated to read the entire sheet document.

Assuming that the reading operation described above is a reading operation at the same magnification, the area that can be read by the CCD unit 18 is actually a wide area as shown in FIG. this is,
This is because the digital color copying machine of this embodiment has a built-in magnification/reduction function. That is, as explained above, since the area that can be recorded by the recording head 37 is fixed at 256 bits at a time, when performing a 50% reduction operation, for example, image information of an area of at least twice as much as 512 bits is required. This is because it is necessary.

(Overall Functional Block Description) Next, the functional blocks of the digital color copying machine of this embodiment will be described using FIG. 9.

Control unit 102. 111. A control circuit 121 controls the scanner section 1, controller section 2, and printer section 3, respectively, and is composed of a microcomputer, a program ROM, a data memory, a communication circuit, and the like.

The control units 102 to 111 and the control units 111 to 121 are connected by a communication line, and the control units 102 . A so-called master-slave control mode is adopted in which the controller 121 performs the operation.

When operating as a color copying machine, the control section 111 performs control operations in accordance with input instructions from the operation section 10 and the digitizer 114.

For example, the operation unit IO uses a liquid crystal as a display unit and is equipped with a touch panel made of transparent electrodes on its surface, so that selection instructions such as color specifications and editing operation specifications can be made. This is the operation section. There are also operation-related keys, such as a key to start copying (start key), a key to stop copying (stop key), and a key to return the operating mode to the standard state (stop key).
Frequently used keys, such as the reset key), are provided separately.

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

The control unit 111 also controls a control circuit (=I/F control unit 112) of a general-purpose parallel interface such as IEEE-488, so-called GP-IB interface, and transfers image data between external devices. Input/output and remote control by external devices can be performed via this interface.

Further, the control unit 111 also controls a multi-value synthesis unit 106, an image processing unit 107, a binarization processing unit 108, a binary synthesis unit 109, and a buffer memory 110, which perform various processes related to images.

The control unit 102 controls a mechanical drive unit 105 that controls the drive of the mechanism of the scanner unit l described above, an exposure control unit 103 that controls the exposure of a lamp when reading a reflective original, and a halogen lamp when using a projector. The exposure controller 104 controls the exposure control section 90. In addition, the control unit 1
02 also controls the analog signal processing section 100 and the input image processing section IO1, which perform various processes related to images.

The control unit 121 includes a mechanical drive unit 105 that controls the drive of the mechanism of the printer unit 3 described above, and a mechanism that absorbs time variations in the mechanical operation of the printer unit 3 and compensates for delays due to the mechanical arrangement of the recording heads 117 to 120. The synchronization delay memory 115 is controlled to carry out the synchronization.

Next, the image processing block shown in FIG. 9 will be further explained in detail along the flow of the image.

The image formed on the CCD 16 is converted into an analog electrical signal by the CCD 16. The converted image information is
The signals are serially processed in the order of red → green → blue and input to the analog signal processing section 100.

The analog signal processing section 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 multi-color signal processing. value (in this example,
The digital image signal is converted into a digital image signal (8 bits long for each color) and output to the input image processing unit 101.

The input image processing unit lot similarly performs correction processing necessary for the reading system, such as shading correction, color correction, and γ correction, on the serial multivalued digital image signal.

The multi-value synthesis section 106 of the controller section 2 is connected to the scanner section l.
This is a circuit block that performs selection and synthesis processing of a serial multi-value digital image signal sent from a serial multi-value digital image signal and a serial multi-value digital image signal sent via a parallel I/F. The selectively combined image data is sent to the image processing unit 107 as a serial multi-level digital image signal.

The image processing unit 107 performs edge enhancement, black extraction, and OCR.

This circuit performs masking processing and the like for color correction of recording ink used in the recording heads 117 to 120.

The serial multilevel digital image signal output is input to the binarization processing unit IO8 and the buffer memory 110, respectively.

The binarization processing unit 108 is a circuit for binarizing a serial multi-level digital image signal to which an error diffusion method is applied. Here, the serial multi-value digital image signal is converted into a four-color binary parallel image signal.

Image data of four colors is sent to the binary synthesis unit 109 and image data of three colors is sent to the buffer memory 110.

The binary synthesis unit 109 combines the three-color binary parallel image signals sent from the buffer memory 110 with the binarization processing unit 1.
This is a circuit for selecting and combining four-color binary parallel image signals sent from 08 to produce four-color binary parallel image signals.

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

The synchronization delay memory 115 of the printer section 3
Absorption of time variations in mechanical operation and recording head 117~
This is a circuit for correcting the delay due to the mechanical arrangement of the recording heads 117 to 120, and internally also generates the timing necessary for driving the recording heads 117 to 120.

The head driver 116 drives the recording heads 117 to 120.
This is an analog drive circuit for driving the recording heads 117 to 120, and internally generates signals that can directly drive the recording heads 117 to 120.

The recording heads 117 to 120 each eject cyan C1 magenta M1 yellow Y1 black ink,
Record an image on recording paper.

(Example of Timing Signal) FIG. 10 is an explanatory diagram of the timing of images between the circuit blocks described in FIG. 9.

Signal BVE is a signal indicating the image valid section for each scan in the main scanning reading operation explained in FIG. Signal B
Full-screen image output is performed by outputting VE multiple times.

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

Signal VCK is a clock signal for sending out image data VD. Signal BVE and signal VE also change in synchronization with this signal VCK.

The signal H8 is a signal used when the valid and invalid sections are repeated discontinuously while the signal VE outputs one line.
If the signal VE is continuously valid while outputting one line, it is an unnecessary signal. This is a signal indicating the start of one line of image output.

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

The color-sequential three-color multi-value image information (cyan C1 magenta M1 yellow Y) sent from the multi-value synthesis unit 106 is converted from the image signal shown in FIG. 1-a to the image signal shown in FIG. 1-b in the scan conversion memory 200. The scanning direction is changed to the image signal of .

The scan conversion memory 200 requires at least a memory capacity equal to or more than one scan of the region (2) in FIG. 1-a. In order to perform high-speed operation, it is necessary to have a memory capacity for two scans of areas ■ and ■, and while writing image data to one bank of the scan conversion memory 200, read converted image data from the other bank. , a so-called double buffer method may be adopted.

The color conversion circuit 201 is a circuit for electrically converting a specific color specified by the digitizer 114 or the like into another color.

By passing through this circuit, it becomes possible to convert a specific color of the original (for example, the color of fabric in a design drawing) into an arbitrary color.

Serial/parallel signal conversion circuit (sp conversion circuit) 2
03 is a circuit for separating color-sequential three-color multi-value image information for each color for color processing in the masking circuit 204 at the next stage.

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

YMC, input data Y'M'C', output data all ~
C33: The correction coefficient black extraction circuit 202 is a circuit for calculating and extracting a black component (black K) from color-sequential three-color multi-value image information.

The color component data having the lowest density value among cyan C1 magenta M1 yellow Y is calculated and extracted as a black component.

The background removal circuit (UCR circuit) 205 is the black extraction circuit 20
The black components and cyan c1 magenta M1 extracted in step 2
Calculation is performed with each component of yellow Y, and processing is performed to improve color reproducibility.By passing through this circuit, color sequential 3
Color multi-value image information (cyan C1 magenta M1 yellow Y
) are four colors in sequence (cyan C1 magenta M1 yellow Y
1 black K).

The background removal circuit 205 may perform gamma correction and image data value offset processing as necessary.

The edge enhancement circuit 206 is a circuit that extracts edge components for each color and performs addition and subtraction on the original image data. It is inserted to improve the reproducibility of fine lines and reproduce images with sharpness. For example, edge components are extracted by 3×3 calculation matrix processing as shown in the following equation.

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

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

This block processing circuit 207 is a circuit for the purpose of erasing band-like striped patterns that occur in highlight areas near areas where the density changes rapidly. For example, an image is divided into blocks like a 4×4 matrix, and a predetermined algorithm is used to detect whether a corresponding block is a highlighted portion. If the corresponding block is a highlighted area, by concentrating the pixel density in the block on a specific pixel and creating pseudo halftone dots, the printing dots are prevented from concentrating, and the generated pattern becomes a band-like striped pattern. to prevent

Next, using FIG. 12, this block processing circuit 20
A specific circuit configuration example of No. 7 will be explained.

The maximum value detection circuit 210 and the minimum value detection circuit 211 are 4×
This is a circuit for detecting the maximum density value D max % and the minimum density value D min of each pixel divided into blocks like a 4 matrix.

The sum calculation circuit 212 is a circuit that similarly calculates the sum D sum of the density values of the blocks of pixels.

Maximum density value D mix, minimum density value Dmin, total sum D
Based on sum, the determination circuit 213 performs determination processing under the following conditions.

D sum < D const+ (= constant) D
mat D min < D const2
(=constant) When both conditions are satisfied, the halftone processing circuit 2
In step 15, pseudo halftone processing is performed on pixels within the block. If the condition is not met, the image data is passed through.

The delay circuit 214 is a line buffer that delays pixels while the above-mentioned determination process is performed. For example, when blocks are formed like a 4×4 matrix, the buffer amount for four lines is sufficient.

In the halftone processing circuit 215, when the above conditions are met,
The following processing is performed on pixels within the block. In this case, the block is assumed to be a 4×4 matrix.

Block A Block B #: Pixel whose density is reduced by a degree *: Pixel whose density is concentrated In order to save all the density data in the block, reduce the density of the # pixel to 1/n, and apply the density to the * pixel by that amount. Make sure to put it on. Since the density data is saved, the advantages of the error diffusion method are not lost through this process.

Concentration distribution and processing blocks also increase the stages of the above judgment,
This may be done in detail.

Alternatively, the blocks may be changed for each color, such as block A1 block B, so that the dots of each color do not overlap.

In other words, the probability that a dot will be hit on a pixel on which a density is applied is high, so by changing the processing blocks like A and B, the density concentration area can be changed, and the probability that dots of each color will be hit on the same area is increased. can be lowered.

By performing such block processing, the printed dots can be dispersed, and it is possible to prevent the occurrence of band-like striped patterns that occur in highlighted areas near the areas where the density changes rapidly.

Next, a specific example of the circuit configuration of the binarization processing section 108 will be described in the first section.
This will be explained using Figure 3-a and Figure 13-b.

Here, the image data is assumed to be a two-dimensional array, and the first image data in the main scanning direction and the first image data in the sub-scanning direction are represented by D+,1.

FIG. 13-b is an error distribution matrix diagram, in which 12 pieces of error data that have been binarized for arbitrary image data Dtj (target pixel) input to the binarization processing unit 108 are divided at a certain ratio. FIG. 4 is a diagram showing the state of the error when the error data is divided into error data and distributed to surrounding pixels. 1 of each error data. , indicates an error occurring in the image data D i,i.

In other words, in this binarization process, errors are accumulated by sequentially shifting the matrix shown in Fig. 13-b one pixel at a time in the main scanning direction, and the total error distributed from multiple pixels is The addition result of the image data inputted as the pixel of interest and 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 section of this embodiment.

In Fig. 13-a, 301 to 310 are delay units consisting of four stages of flip-flops, and in order to process image data in color sequence (cyan, magenta, yellow, black) for each color, each In the delay section, data is delayed by four clocks to delay one pixel.

311 to 322 are adders. The adders 311 to 321 add and subtract error data to each other in order to perform error calculations in the error diffusion matrix, and the adder 322 adds and subtracts error data that is the result of error calculations in the error diffusion matrix. It performs addition and subtraction on input image data.

323 and 324 are, for example, FiFo (first
This is an error line memory using an in-first-out (in-first-out) memory, which stores the error calculation results for each line and delays by one line.

Reference numeral 325 denotes an error distribution section consisting of a ROM (read only memory). 326 is a comparator that compares the result of addition of the error data and image data with a set threshold value. Multi-valued image information of four colors sent from the comparator 326 (cyan C1 magenta M1 yellow Y1 black K)
The scan conversion memory 300 changes the scanning direction from the image signal shown in FIG. 1-b to the image signal shown in FIG. 1-a. This is a change in scan direction that is the opposite of the operation in scan conversion memory 200.

The scan conversion memory 300 includes at least
It requires a memory capacity 1 which is equal to or more than the area l scan, but unlike the scan conversion memory 200, even if the number of images to be handled increases by one color (black K), it is a binary image, so the memory capacity is small. Similar to the scan conversion memory 200, in order to perform high-speed operation, it has a memory capacity for two scans of the areas ■ and ■, and when writing image data to one bank of the scan conversion memory 200, it It is sufficient to adopt a so-called double buffer method in which the converted image data is read out.

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

The image data input to the binarization processing unit 108 is first
Error data output from delay section 310 and adder 322
are added and input to the error allocation section 325. The error allocation unit 325 uses a look-up table in the ROM to calculate error data (
output a+ bl C, d). Also, the adder 322
The output is compared with a preset threshold value by a comparator 326, and a binary output of 1 or 0 is performed. The binarized output of the comparator 326 is input to a gate section 327, and only the required pixels are output.

Here, image data D1. ．． error allocation unit 325 for
The error data output from a j i , bl,
l, CI.

1+ di, I, the error data d L I is delayed by four colors in the delay unit 301, and then becomes the image data D I+
Error data Cill of the same color occurring in the pixel of Li,
l and an adder 311.

From then on, similarly 302.312.303.313.304
After the errors are sequentially added at 314, the output of the adder 314 is input to the line memory section 323. The stored error addition data is read out after being delayed by one line in the line memory section 323. The read error addition data is input to the adder 315.

Thereafter, similarly 305.316.306.317.307
At 0.318, 308.319, error data caused by other pixel data is sequentially added. The adder 319 collects error data C++4.1++ generated from input image data D++4.1++. +
After +1 is added, it is input to the line memory section 324. The error data output from the line memory section 324 is added to the error data by adders 320 and 321, and then
The adder 322 adds it to the image data. Next, the result of addition of the error data and the image data is input to the error allocation section 325 and the comparator 326. Thereafter, the binarization process is performed sequentially as before.

Taking input image data n, 1 as an example, the processing explained above is
Expressed as a formula, it becomes as follows.

D D +, i = D t, j Toyama-2, I-z +c+-+, +-2+b+, r
z +C++1. i-2 Toyama+2. r2+Cl-2,
1-1+b+ -+, j-+ +a+, 1-+ +
b++ t 1-+ +c++z, 1- +10b+-
2.3+a+-+, I DD: Data after calculation D = image data, pixel number in the second line (by color) j second line number Next, we will explain the specific operation of the circuit in Figure 13, and the timing in Figure 14.・Explain using a chart.

FIG. 14 is a diagram showing the timing of single color data to simplify the explanation.

The signal VEI is a main scanning interval signal in FIG. 1-b.

The circuit operation described above is performed while the signal VEI is valid, and the calculation result data is input to the scan conversion memory 300 and stored.

In the scan conversion memory 300, a signal VE2 corresponding to the main scanning section signal of FIG. Output to.

The error data at the boundary of the area in Figure 1-a is the line
Since the data will be stored in the memory units 323 and 324, there is no need to be particularly aware of the error data at the boundary of the area.

Next, using FIG. 18, scan conversion memory 200.3
An example of signal conversion in 00 will be explained. The scan conversion memories 200 and 300 have two memories a and b as shown in the figure.
It is assumed that it is divided into banks.

First, at 5TEPI, an image is written to memory bank a of scan conversion memory 200. Next, 5TE
After P2, data is sequentially written into memory banks a and b alternately, such as memory bank b1 memory bank a.

During this time, as seen from 5TEP2 onwards, signals whose scan directions have been converted are read out one after another from the scan conversion memory 200, and after being subjected to the binary processing described above, they are sequentially converted into binary data in the scan conversion memory 300. The image data is written.

After 5TEP3, the scan conversion memory 300 outputs a binary image signal whose scan direction has been returned as shown in the figure.

In this way, by adopting the double buffer method,
It can be seen that scan conversion of image data is performed at high speed.

[Other possible embodiments]

In this embodiment, table conversion using a ROM is used in the error allocation section 325, but it goes without saying that a RAM, a multiplier, etc. may also be used.

In addition, in this embodiment, the scan conversion memory 200.30
0 has been shown, but it is also possible to use only the scan conversion memory 200 and output the scan-converted signal directly to an LBP (laser beam printer), etc. for recording. good.

FIGS. 15 to 17 are diagrams showing other examples of image output that require image connection information when the error diffusion method is applied.

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

In this example, in addition to the image connection part explained above, 1, 2,
In the portions indicated by broken lines in each of the output images 3 and 4, new image connection information is required.

FIG. 16 shows that when cut paper is used in the copying machine described above, or when cut paper is similarly used in a copying machine using a printer such as LBP, one document is printed on printed paper. This is an example of enlarging continuous shooting into four images.

In this example, a portion requiring new image connection information occurs in the portions indicated by broken lines in images 1, 2, 3, and 4 of the original. That is, in printed paper, the counterfeit areas where the images touch are the areas where image linking information is required.

FIG. 17 is an example showing where images are joined when images are combined in the copying apparatus described above.

This is an example in which copying is performed on print paper as shown in the figure, in which the document area indicated by A-B is scaled. In this case, At, Bl, A
2. If copies are made in the order of B2, an image connection will occur at the boundary shown by the broken line on the printed paper. However, in this example, unlike the above example, AI, Bl
, A2. In order to copy like B2, it is necessary to separately manage information on image connections at the boundaries of A1 and A2, and the boundaries of B1 and B2.

By applying the present invention to any of the examples shown in FIGS. 15 to 17, the problem of image connection when applying the error diffusion method can be solved.

As explained above, by converting the scan direction,
It can be seen that a smooth image output without seam lines is obtained, and the intended purpose of the present invention is achieved.

Further, according to this embodiment, data writing to memory,
By changing the reading order, bidirectional scan reading and bidirectional printing become possible.

In other words, in FIG. 8, when the scan of the area (■) is completed, instead of returning to the correction area 68, the area is scanned in the opposite direction to that shown in the figure, and the signal is reversed by the scan conversion memory, so that the scan in both directions is performed. Scan reading becomes possible.

In FIG. 8, when the scanning carriage 34 returns to direction B, by reversing the signal in the scan conversion memory,
Bidirectional printing is possible.

This can be done by simply using a counter that can switch up/down address control for writing and reading from the scan conversion memory.

This bidirectional scan reading and bidirectional printing is
Since the time required to return to the position can be shortened, faster copying operations are possible.

Furthermore, by using this function, mirror image processing can be easily performed by switching up and down the address control for writing and reading.

〔effect〕

As described above, according to the present invention, since the error diffusion method is performed after image data is once stored in the memory, it is possible to prevent the occurrence of streaks at the boundaries of the image.

[Brief explanation of the drawing]

FIG. 1-a and FIG. 1-b are diagrams showing an example of image processing for explaining the problem to be solved by the present invention. FIG. 2-a and FIG. 2-b are diagrams for explaining in detail the problems to be solved by the present invention. FIG. 3 is a diagram for explaining the present invention in detail. FIG. 4 is an external view of a digital color copying machine to which the present invention is applied. FIG. 5 is a sectional view from the side of the digital color copying machine shown in FIG. FIG. 6 is a detailed explanatory diagram of the scanning carriage 3 and the invention. FIG. 7 is a diagram for explaining the mechanical mechanism inside the scanner section l. FIG. 8 is an explanatory diagram of reading operation in book mode and sheet mode. FIG. 9 is an explanatory diagram of functional blocks of a digital color copying machine to which the present invention is applied. FIG. 1O 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 diagram showing an example of a specific circuit configuration block of the binarization processing section 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 examples of image output requiring image connection information. FIG. 18 is a diagram for explaining signal conversion.

Claims (2)

[Claims] (1) An image processing method characterized by storing image data spanning a plurality of divided scan areas adjacent to each other in a memory, and then processing the image data stored in the memory by an error diffusion method. (2) The image according to claim 1, wherein the error diffusion method distributes error data generated during image binarization processing to surrounding pixels to reproduce a halftone image. Processing method.