JP3189449B2 - Image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus,
In particular, the present invention relates to an image processing apparatus that forms an image by reproducing density data of each pixel using a laser beam.

[0002]

2. Description of the Related Art In a recording apparatus of a scanning recording type, various methods are adopted to digitally reproduce the density of an image. Such digital tone reproduction methods include a dither method, an intensity modulation method, and a pulse width modulation method. In the dither method, a plurality of pixels are taken as one unit, and the on / off area ratio of the pixels included therein is changed to express the density of an image. In the intensity modulation method, the light emission intensity of the laser is modulated in multiple stages for one pixel, the laser energy is radiated to the inside of the pixel on average, and the density is changed. The pulse width modulation method modulates the light emission time per unit pixel while keeping the light emission intensity of the laser constant. For example, Japanese Patent Application Laid-Open Nos. Sho 61-225971 and Sho 62-1169.
No. 59 discloses this.

[0003]

In the dither method, moiré noise peculiar to the dither method is generated because a plurality of pixels are regarded as one unit, and the image quality is degraded.

In the intensity modulation method, density can be basically output one-to-one according to read image data, and high resolution and fine smooth gradation characteristics can be obtained. However, in the highlight portion, fine density control is required, and therefore, the gradation reproducibility is difficult. Further, there is a problem that the graininess of the halftone portion is noticeable due to the influence of the base of the image recording paper.

On the other hand, in the pulse width modulation system, although the problem of granularity in the intensity modulation system has been improved, it is generally employed because the center of gravity of a pixel is moved in units of two pixels, and therefore, for example, a density of 400 DPI is used. When the data is reproduced, the reproducibility is substantially 200 DPI, and the resolution is reduced. On the other hand, if the pulse width modulation method is adopted for each pixel, the emission time of the laser is considerably reduced in a pixel having a low density, and the image quality is not stable in terms of toner adhesion.

In order to solve such a problem, the applicant of the present application has proposed an image processing apparatus using so-called line screen processing in Japanese Patent Application No. 3-359082.

However, if the line screen processing is uniformly performed regardless of the type of the original, for example, in the case of an original in which a photographic image and a character image are mixed, patterning is performed by the line screen processing in the character portion. Is not preferred. In order to prevent this, a method of judging the type of the document image and switching the execution of the process can be considered. However, the process suddenly changes at the boundary where the type judgment (area discrimination) changes. This results in a reproduced image with a strange feeling.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and provides halftone processing while maintaining continuity of processing at a boundary where the type of image in a document image changes and maintaining resolution. It is an object of the present invention to provide an image processing device that improves the granularity of a part.

[0009]

According to the present invention, there is provided an image processing apparatus, comprising: a receiving unit for receiving image data read for each pixel; and processing data processing means to transferred to the image data of the pixel adjacent to each other
Calculation means for calculating the difference between
If the difference is larger than a predetermined threshold value, the image data processed by the data
Image data without processing by data processing means
And a data output means for outputting. Preferably, the data processing means transfers the image data of one adjacent pixel to the image data of the other pixel based on a value determined according to a difference between the image data of the adjacent pixels. An image processing apparatus according to another aspect of the present invention is a receiving unit that receives image data read for each pixel, and converts the received image data such that image data of one pixel in adjacent pixels is an image of another pixel. Data processing means for processing the data to be transferred to data, data output means for outputting the processed image data, and a difference between the image data of one pixel and the image data of the other pixel is equal to or greater than a first predetermined value. In the case where the first control means controls the data processing means so as not to process the image data, the difference between the image data of one pixel and the image data of the other pixel is less than a first predetermined value. In this case, a second predetermined value determined by the average value of the image data of the adjacent pixel is added to or subtracted from the image data of each pixel constituting the adjacent pixel, and the image changed by the second predetermined value is obtained. And a second control means for controlling the data processing means to process data as image data received.

[0010]

According to the present invention, the data is processed so that a part or all of the received predetermined image data is transferred to the image data of the adjacent pixel. Also, the adjacent image
The difference of the image data between the elements is calculated and calculated.
Image data is output based on the difference.

[0011]

FIG. 1 is a sectional structural view of a digital copying machine main body according to an embodiment of the present invention.

Referring to FIG. 1, a printer body 1 includes a desk 4
The photosensitive drum 10 is set at substantially the center so as to be rotatable in the direction of arrow a. Around the photosensitive drum 10, a charging charger 11, magnetic brush type developing devices 12 and 13, a transfer charger 14, a paper separating charger 15, a cleaning device 16 for residual toner, an eraser lamp 17 for residual charge, and the like are provided. . The image is exposed on the photosensitive drum 10 by the laser beam scanning optical system 2 immediately after the charging process. Since the printing process using these elements is well known, the description is omitted.

On the other hand, on the left side of the printer body 1 in the figure, three automatic paper cassettes 21, 22, and 23 are provided, and an optional automatic paper feed unit 24 of an elevator type is installed on a desk 40. . The size or weighing of the paper loaded in each cassette and paper feeding unit is detected by sensors SE11 to SE14, respectively. Sheets are selectively fed one by one from each cassette and a sheet feeding unit by respective sheet feeding rollers 25 to 28. The bold line in the drawing indicates a paper passing path, and each sheet is held at one end by a timing roller 30 and sent to a transfer section in synchronization with an image formed on the photosensitive drum 10.
The sheet after the transfer of the toner image is conveyed to a fixing device 32 by a conveying belt 31, where the toner is heated and fixed.
The sheet is discharged from the discharge roller 33 to the outside of the main body, and is introduced into the sheet reversing unit 50.

The paper reversing unit is a roller 3 for a double-sided printer that prints on the other side of the single-sided printed paper or a composite print that prints over the same side.
6 and 37, and a face-up discharge (non-reversal mode) for conveying the paper straight to the paper discharge tray 60, and a face-down discharge (non-reversal mode) for reversing the paper. (Reversal mode).

In order to achieve the above functions, the sheet reversing unit includes a receiving roller 51, a sending roller 52, forward / reverse switching rollers 53 and 54, and a switchback path 5.
Eight. The switching claws 56 and 57 can be switched between two rotation angles by a solenoid (not shown).

In the non-reversing mode, the sheet is guided from the receiving roller 51 on the upper surface of the switching claw 56, and sent out from the sending roller 52 to the sheet tray 60 in a face-up state. In the reversing mode, the sheet is guided from the receiving roller 51 on the left side surface of the switching claw 56, and the forward end of the sheet reaches the switchback path by the normal rotation of the roller 54. When the trailing edge of the sheet reaches the reversal point Q, the rollers 53 and 54 are switched to reverse rotation. here,
The sheet is guided by the right side of the switching claw 56 with the rear end up to that point as the leading end, and is sent out from the sending roller 52 to the sheet tray in a face-down state.

On the other hand, in the double-sided printing mode, the sheet is conveyed to the switchback path in the same manner as in the reversing mode. Here, the sheet is guided by the lower left surface of the switching claw 57 with the rear end up to that point as the leading end,
The sheet is fed from the sheet re-feed rollers 36 and 37 to the sheet re-feed path 35. In the composite print mode, the paper is
From 3, the sheet is guided by the upper left surface of the switching claw 57, and is fed from the re-feed rollers 36 and 37 to the re-feed path 35.

An image reader (IR) optical system 110 exposes and scans a document placed on a document table glass 118, and converts reflected light from the document to electric signals by photoelectric conversion elements 116 and 117 using, for example, a CCD array. It is something to convert. The photoelectric conversion elements 116 and 117 convert an image of a specific color such as black, for example, and an image of another color such as red into electric signals, respectively.

An image reader (IR) optical system 110 is attached to a scanner 119 which is moved in parallel with a platen glass 118 by a scan motor M2, and an exposure lamp 111 for irradiating a document and a reflection mirror 112 for changing the direction of light reflected from the document. , Two mirrors 113a and 113b for changing the optical path from the reflection mirror 112, a lens 124 for condensing the reflected light, and a color discrimination based on the wavelength of the reflected light, and reflecting or transmitting the color to obtain two photoelectric conversion elements. 11
A half mirror 115 for guiding reflected light to 6 and 117;
Photoelectric conversion element 1 generated by an electric signal according to received light
16 and 117, and performs exposure scanning of the original when the scanner 119 moves leftward as indicated by the arrow.

FIG. 2 is a perspective view showing the configuration of the laser optical system in the optical unit 2 of FIG.

Referring to FIG. 1, a laser beam emitted from semiconductor laser element 161 in response to a drive signal passes through collimator lens 155 and cylindrical lens 153 and enters one surface of polygon mirror 152. The beam reflected by this surface passes through the f-θ lens 156, is reflected by the mirror 159, goes out of the optical unit 2 through the slit 114, enters the photosensitive drum 10, and exposes the photosensitive drum 10. As the polygon mirror 152 rotates, the emission direction of the beam reflected from one surface of the polygon mirror changes as shown in the figure, and the photosensitive drum 10 is scanned in the axial direction. At the start of the scan to synchronize this axial scan, the laser beams are mirrored 158 and 16
0, reflected by photodiode (SOS sensor) 16
3 is incident. When disposing the optical system, mirrors 158 and 160 and photodiode 163 are arranged such that the optical path length from polygon mirror 152 to photodiode 163 is substantially equal to the optical path length from polygon mirror 152 to photoconductor drum 10. You.

FIG. 3 is a block diagram showing the configuration of the entire system of the digital copying machine shown in FIG. Referring to the figure, a control processor 20 for controlling the printer main body is provided on the printer side.
0, a control processor 201 for controlling an image reader (IR) optical system, a control processor 202 for controlling a paper feed option if there is one, and a control processor 203 for controlling the paper discharge option if there is one. The print information is transmitted from the optical system control processor 201 to the printer main body control processor 200 via the line screen processing processor 204 which performs density data processing.

A signal such as a print mode is transmitted to the interface control processor 215 via the control line 214. This interface control processor 215
Communicates with the processors 200 to 203 in various modes via the serial interface 216. Further, the interface control processor 215 operates the operation unit 2.
The control unit 18 receives an input from the control unit 18 and controls on / off of the operation panel display unit 217 on the printer body. The display unit displays various information based on an instruction from the processor 215.

The operation unit 218 is provided with a changeover switch 219 for switching the processing mode. That is, the switch 218 switches between a mode in which line screen processing described below is performed and a mode in which normal processing is performed. Switching the processing mode in this way is sometimes suitable for processing a document in which characters occupy most, for example, while normal processing may be more suitable for a document in which characters and photographs are mixed. This is because the line screen processing may be preferable in terms of quality in the processing for. In this manner, optimal processing according to the type of the original is enabled.

FIG. 4 is a flowchart showing a main routine of the interface control processor 215 shown in FIG.

First, initialization is performed in step S300, and the internal RAM and the like are cleared. Next, serial data is received (S301), and conditions such as a print mode setting and a print request are set. Next, in step S302, it is determined whether a print request has been issued. When there is a print request, the print processing (S30)
Perform 3). Specifically, launch around P / C,
Execution of sheet feeding and control of rollers and the like are performed.

Next, normal processing is performed in step S304, and this processing is performed regardless of whether the apparatus is in a printing mode or a standby mode. Thereafter, information such as the print sequence and status of the printer main body control processor 200 is sent to the interface control processor 215 by serial transmission (S305).

Finally, one loop counter is checked for increment (S306), and the flow returns to step S301.

FIG. 5 is a system configuration diagram around the line screen processor 204 of FIG.

Referring to the figure, image data (8 bits) read by image reader IR is written into first memory (FIFO) 250 line by line. Along with the image data, a main scanning valid signal A indicating the presence of a document in the main scanning direction shown in FIG. 8 is also sent from the image reader IR, and the signal is sent to the timing controller 252 and the first memory 250.
Is input to A sub-scanning effective area signal indicating the presence of a document in the scanning direction shown in FIG. After a predetermined time, the timing control unit generates a main scanning effective area signal B,
It is provided to the processor 204 and the first memory 250. With this signal, the processing shown in the flowchart of FIG. 7 (described later) is executed, and the image data for one line is processed for each window corresponding to every two pixels as shown in FIG. Then, the image data for every two pixels processed by the line screen processor 204 is written to the second memory 251. The processed image data stored in the second memory is output as 8-bit image data to the printer control processor at the timing of printing, and the laser printer forms an image based on the data.

FIGS. 6 and 7 are flowcharts showing the control contents of the print processing performed by the line screen processor 204 of FIG.

Before describing this flowchart in detail, an outline of the control will be described with reference to FIGS.

FIG. 8 is a diagram showing the ON / OFF relationship of the main scanning direction effective area signal and the sub-scanning effective area signal for the original to be read. As shown in the figure, the main scanning effective area signal is a signal that changes when a document is present in the line direction with respect to the document, that is, in the main scanning direction. On the other hand, it is a signal that changes when a document exists.

FIG. 9 is a diagram showing the relationship between the main scanning effective area signal, each image data, and the window number. In the figure, as an example, one line of image data is described for N + 1 pixels from 0 to N. One window number is assigned to each two adjacent pixels. That is, the window number W0 corresponds to the image data 0 and 1, and the window number W (N-1) / 2 corresponds to the image data N-1 and N. For convenience of the following description, image data 0 is a window W
0 corresponds to left density data L, and pixel data 1 corresponds to W
This corresponds to right density data R of 0. Similarly, the pixel data N-1 corresponds to the left density data L of W (N-1) / 2 and the image data N corresponds to the right density data R of W (N-1) / 2.

FIG. 10 is a schematic diagram showing the procedure of processing the density data for each pixel. FIG. 10A shows the basic concept of processing density data according to the present invention. In the figure, the vertical axis indicates 256 gradations (0 to 25).
5) is shown, and the horizontal axis shows left density data L and right density data R of a certain window. In this example, the density value of the left density data L is large, and there is a difference from the density value of the right density data R by the value _DLR . Is smaller than the threshold D _TH there is this difference D _LR, the value of the right density data R is, on the left density data L, are moved as indicated by the broken line. In this example, as a result, the left density data L
Increases to the position indicated by the broken line, and the value of the right density data R becomes 0
Becomes

In the case (2) of FIG. 10, the processing is shown in the case where the difference _DLR between the left density data and the right density data is larger than the threshold value _DTH . In this case, FIG.
The transfer of density data as shown in (1) is not performed.
The reason why the relocation is not performed is that, for example, in the case of an image such as character data in which an edge portion is clearly shown, if the relocation is performed as shown in FIG. 10A, the position of the edge portion moves. This is because the reproducibility of the image is not preferable.

FIG. 10C shows another example of the transfer of image data. In this example, the difference D _LR between the left density data L and the right density data R is the threshold value D _TH
Therefore, the transfer of the density data is basically performed as shown in (1). However, in this example, since the value of the left density data L is large, if all the values of the right density data R are relocated, the value exceeds the maximum density level 255.
Therefore, in this case, the transfer amount is determined from the right density data R as indicated by the broken line so that the upper limit of the left density data L becomes the maximum value 255. Therefore, as a result of the relocation, the value of the left density data L becomes the maximum value 255, the value of the right density data R does not become 0, and remains as the density data at the position indicated by the broken line. By doing so, the amount of toner adhered to the pixel corresponding to the left density data L becomes the maximum value, and the density level of the whole pixel constituting this window is maintained.

FIG. 11 shows the result of the data transfer shown in (1) of FIG. 10 in the windows W0 to W4 and the first line.
FIG. 6 is a diagram showing the states of pixels in portions corresponding to FIGS.
As shown in the figure, in this example, all the right density data R are moved to the left density data L, so that the densities of the pixels constituting each of the windows W0 to W4 are all moved to the left pixel L. As a result, line screen processing in which every other pixel is emphasized is performed. In this example, the value of the right pixel R after the relocation is set to 0. However, even when the relocation as shown in (3) of FIG. 10 is performed, the density of the left pixel L is emphasized. As a result, the same effect as when the line screen processing is performed is produced.

Next, the flowcharts of FIGS. 6 and 7 will be described. When the line screen processor starts processing, first, in step S501, it is determined whether the sub-scanning effective area signal has changed. When the sub-scanning effective area signal has not changed, that is, when the optical system is not reading a document, the process returns as it is. On the other hand, if it is within the sub-scanning effective area, it is determined in step S502 whether the main-scanning effective area signal has changed. When this signal changes, it means that the optical system has started scanning the original in the main scanning direction. Therefore, the window number is reset to 0 in step S503. on the other hand,
If the main scanning effective area signal has already been changed, the flow jumps from step S503 and proceeds to step S504. In step S504, it is determined whether the document to be read is within the main scanning effective area. If it is out of the area, the program returns without performing line screen processing.

If the object to be scanned by the optical system is within the main scanning effective area, an even-numbered pixel among the pixels stored in the first memory 250 is read into the line screen processor 204 in step S505. . That is, the data of the (window number × 2) -th pixel is stored in the left image data L. Next, in step S506, the odd-numbered pixels in the image data stored in the first memory 250 are read. That is, in the right image data R,
The data of the (window number × 2 + 1) -th pixel is stored.

Next, in step S507, step S50
In steps 5 and 506, the absolute value of the difference between the stored image data L and image data R is calculated. That is, step S
In step 507, a process for determining the variation in density data between adjacent pixels is performed.

Next, in step S508, it is determined whether or not the obtained difference is smaller than a predetermined value. If the difference is not less than the predetermined value, it corresponds to the state of (2) in FIG. 10 and the flow returns to step S514. In this case, since the image data is not relocated, the values of the image data L and R read from the first memory 250 are output to the second memory 251 as they are, and stored there. Then, in step S515, the window number is incremented in order to process the image data for the next window, and then the flow returns to step S504.

On the other hand, if the difference is smaller than the predetermined value in step S508, the flow proceeds to step S50 to process the image data (1) or (3) in FIG.
Go to 9 or less. In step S509, the image data L
, A value obtained by adding the image data L and the image data R is stored. Then, in step S510, the image data L
Is greater than the maximum value, that is, 255 in FIG. If the image data L does not exceed the maximum value, a value of 0 is stored in the image data R in step S512 in order to process the image data as (1) in FIG. Then, the image data L and R determined in steps S509 and S512
Is output and stored in the second memory 251 in step S514, and after the window number is incremented in step S515, the flow returns to step S504.

On the other hand, in step S510, step S5
If the image data L obtained in step S09 exceeds the maximum value, processing corresponding to (3) in FIG. 10 is performed. That is, in step S511, a value obtained by subtracting the maximum value from the image data L is stored in the image data R. That is, as shown in (3) of FIG. 10, this is a process of calculating the value of the position of the broken line of the right image data R. Then, in step S513, the maximum value 255 is stored in the image data L. Thereafter, similarly, the processing from step S514 is performed, the window number is incremented so as to process the image for the next window number, and the flow returns to step S504.

FIG. 12 is a diagram showing an evaluation of granularity of an image formed by applying one embodiment of the present invention in consideration of visual characteristics. On the other hand, FIG. 13 is a diagram showing a granularity evaluation for an image formed by the conventional intensity modulation method, and corresponds to FIG. In both figures, the horizontal axis shows the spatial frequency, and the vertical axis shows each power corresponding to the spatial frequency. As shown in FIG. 12, in FIG. 12, power is concentrated around a spatial frequency of 4 (lp / mm), while in FIG. 13, in a low frequency component of a spatial frequency of 4 (lp / mm) or less. The state where noise is occurring is shown.

FIG. 14 shows the MT of vision according to Dooley, which shows the effect of spatial frequency as noise on vision.
It is an F characteristic view.

In the figure, the horizontal axis indicates the spatial frequency, and the vertical axis indicates the level indicating the effect on the visual sense as noise. As the value approaches 1, the human eye sees Noise, that is, a decrease in image quality is felt. As can be clearly seen from FIG. 14, the maximum noise effect is shown at the value of the spatial frequency 1 (lp / mm). When the granularity evaluation of FIGS. 12 and 13 is performed based on FIG. 14, the effect of the line screen processing of the embodiment according to the present invention is remarkably exhibited. That is, according to the embodiment of the present invention in FIG.
While the component per (lp / mm) is extremely small,
In the case of the conventional intensity modulation method shown in FIG. 13, it can be seen that the components are concentrated around a spatial frequency of 1 (lp / mm).

FIG. 15 is a photographic image of 16 gradations read to show the effect of one embodiment of the present invention. FIG. 16 is a diagram of the original image shown in FIG. It shows an image as a result of performing a line screen process. In FIG. 16, the processing is such that the direction of the line screen is indicated in the vertical direction of the figure.

FIG. 17 shows a document read in order to show the effect of one embodiment of the present invention on a character image. FIG. 18 is an image according to an embodiment of the present invention when the line screen direction is given to the document of FIG. 17 in the right direction with respect to the drawing. FIG. 19 is a diagram illustrating the line screen direction. 5 is an image according to one embodiment of the present invention when given in the vertical direction with respect to.

FIG. 20 shows a conventional image when the so-called dither method is applied to the original shown in FIG. In FIG. 20, it can be seen that data to be connected and reproduced like characters is reproduced discontinuously by dither processing. On the other hand, as shown in FIGS. 18 and 19, according to the embodiment of the present invention, even more excellent image reproduction can be performed for a character image. FIG. 21 corresponds to FIG. 11, in which the direction of the line screen is changed to a direction of 45 degrees. Specifically, for line 1, the window W
0 to W4, the right pixel R
Then, the data is transferred to the pixel L on the left side, and the processing for transferring the data of the pixel on the left side to the pixel on the right is performed on the line 2. In this way, by reversing the direction in which the pixels are transferred depending on the odd and even numbers of the lines, the arrangement of the pixels having the emphasized density among the adjacent pixels has a checkered pattern, that is, a screen angle of 45 degrees. FIG. 23 shows an image reproduced from the document image of FIG. 15 at the screen angle of 45 degrees.

FIG. 22 is a further modified example of FIG. 11 in which the direction of pixel shift is further changed. In this example, for lines 1, windows W0, W2 and W
The pixel data is relocated to the left only for No. 4, and no pixels are relocated for windows W1 and W3. Next, for line 2, the windows W1 and W3
, But not for windows W0, W2 and W4. Line 3
Is performed by performing the same transfer as that of the line 1, thereby creating a pixel pattern that emphasizes the density as shown in the figure. As a result, the screen angle becomes 26.6 degrees, and the effect is shown in FIG. 24 as an image read from the original in FIG.

FIG. 25 is a flowchart showing the control contents of the line screen processor when the line screen processing is performed on three adjacent pixels according to another embodiment of the present invention.

The process of transferring the density data to three adjacent pixels is specifically shown in FIG.

As shown in FIG. 27A, the center image data M, the image data L adjacent to the left side thereof, and the image data R adjacent to the right side thereof are as shown in FIG. Suppose you have a value. In this case, the image data having the maximum density data among the three adjacent pixels, ie, in this example, the image data L and the adjacent three pixels
Image data having the minimum density data among the pixels, that is, in this example, a difference from the image data M is obtained. If this difference D is smaller than the threshold value D _TH ,
For the central image data M, the image data L on both sides
And density data of R are transferred. In this example, the value of the image data L is superimposed on the value of the image data M,
Further, the value of the image data R is superimposed thereon,
If all the image data are stacked on the central image data M, the density data exceeds the maximum value 255 of the density data. Therefore, the portion exceeding the maximum value is distributed and remains as the values of the image data L and R. .

On the other hand, as shown in FIG. 27B, the difference D between the density data of the pixel indicating the maximum density and the value of the pixel indicating the minimum density data among the three adjacent pixels.
Is larger than the threshold value D _TH , the density data transfer processing is not performed as in the previous embodiment. The reason for this is the same as in the previous embodiment, in order to prevent the possibility of edge relocation or the like occurring in the character image.

Returning to the flowchart of FIG. 25, the description of the other embodiment will be made below. However, since the processing from step S601 to step S604 is the same as that of the previous embodiment, the description will not be repeated here.

In step S605, the image data L is stored in the pixel data stored in the first memory 250 as
The data of the (window number × 3) -th pixel is read and stored.

In this embodiment, the window numbers correspond to every three adjacent pixels, and are different from the window numbers corresponding to every two adjacent pixels in the previous embodiment.

Next, in step S606, the image data M
Then, from the first memory 250, (window number × 3 +
1) Read and store the data of the pixel. Similarly, in step S607, the image data R is stored in the first memory 25.
From 0, the data of the (window number × 3 + 2) th pixel is read and stored. Next, in step S608, the largest one of the data stored in the image data L, M, and R is set to data A, and similarly, in step S609, the smallest one of the three data is set to data B. Then, in step S610, the difference between the data A and the data B is calculated.
In step S611, it is determined whether the difference is less than a predetermined value. If the difference is less than the predetermined value,
In order to perform the density data transfer processing shown in (1) of FIG. 7, the flow proceeds to the flow from step S612. If the difference is not less than the predetermined value, as shown in (2) of FIG. Since the transfer of the density data is not performed, the flow proceeds to step S619. In step S619, the values of the image data L, M, and R are output as they are, and stored in the second memory 251. Then, in step S620,
After incrementing the window number in order to perform processing for the next window, the flow returns to step S604.

On the other hand, if the difference is smaller than the predetermined value in step S611, the image data M
In which all the values of the image data L, the image data M and the image data R are added. And step S
At 613, it is determined whether or not the image data M is larger than the maximum value, that is, 255. If the image data M does not exceed the maximum value, a value of 0 is stored in the image data L in step S617, and a value of 0 is stored in the image data R in step S618, and then the flow proceeds to step S619.

On the other hand, in step S613, the image data M
Is larger than the maximum value, in step S614,
A half value of the value obtained by subtracting the maximum value from the image data M is stored in the image data L. And step S615
Then, a value obtained by subtracting the maximum value and the image data L from the image data M is stored in the image data R. Further, step S616
Then, the maximum value is stored in the image data M. That is, when the value obtained by adding the density data of the three adjacent pixels exceeds the maximum value by the processing from step S614 to step S616, the value of half of the value exceeds the maximum value.
The image data is distributed to the left and right image data L and R.

As described above, the values of the image data L, M and R are determined, and the values are output to the second memory 251 and stored in step S619. Then, in step S620, after the window number is incremented in order to process the pixel corresponding to the next window, the flow proceeds to step S604, and thereafter, the same processing as described above is performed.

In the first and second embodiments,
Although the direction in which the line screen is added is the main scanning direction, it can be added in the sub-scanning direction. However, since the sub-scanning direction is easily affected by errors in the rotation pitch of the photosensitive drum, it is preferable that the main scanning direction be the screen direction.

In the first and second embodiments,
Although the threshold value for determining whether or not to execute the transfer of the density data of the pixels is fixed, the threshold value may be changed depending on the state of the read image, for example, according to a halftone image or a character image. .

Further, the specific value of the threshold value is 0 to 2
In the case of 55 gradations, about 80 is desirable. In this case, the contrast difference between white and black is about 240, which is set to about one third thereof.

Further, in the first and second embodiments, the density data is transferred to two or three adjacent pixels. However, depending on the original image, four or more adjacent pixels are transferred. It is also possible to transfer density data.

Further, in the first and second embodiments, the present invention is applied to an image processing apparatus using an intensity modulation method. However, the idea of the present invention can be applied to methods other than the intensity modulation method. Needless to say.

Further, in the first and second embodiments, when transferring the density data, the upper limit is set to the maximum value 255.
However, it is not always necessary to set the upper limit to the maximum value, and it is also possible to transfer the density data by setting a value less than the maximum value as the upper limit.

In the first and second embodiments,
Although the processing of density data is performed on each of two adjacent pixels and three adjacent pixels, any of those processes may be configured to be performed by one digital copying machine. In this case, as shown in FIG. 32, a switch 220 for switching the type of processing may be provided in the operation unit 218 separately from the switch 219 so that any one of the processings can be designated.

Instead of providing the switch 220, the processing mode is designated by the switch 219, whereby the line screen processing for two pixels or the line screen processing for three pixels is performed. May be determined. That is, normal processing is performed in the processing mode for a document with most characters, and 2 in the processing mode for a document in which characters and photographs are mixed.
The line screen processing may be performed on the pixels, and the line screen processing may be performed on three pixels in the processing mode for most originals of a photograph.

FIGS. 28 and 29 are flowcharts showing the control contents of the line screen processing processor when the line screen processing is performed on three adjacent pixels according to the third embodiment of the present invention.

The process of transferring the density data to three adjacent pixels is specifically shown in FIG.

As shown in FIG. 30A, the center image data M, the image data L adjacent to the left side thereof, and the image data R adjacent to the right side thereof are as shown in FIG. Suppose you have a value. In this case, the image data having the maximum density data among the three adjacent pixels, that is, the image data L in this example,
Image data having the minimum density data among the pixels, that is, in this example, a difference from the image data M is obtained. When the difference D is smaller than the second predetermined value _DTH , the density data of the image data L and R on both sides of the central image data M is transferred. In this example, the value of the image data L is superimposed on the value of the image data M, and the value of the image data R is further superimposed on the value. Since the data exceeds the maximum value 255, the portion exceeding the maximum value is evenly distributed to the image data L and R.

On the other hand, as shown in (2) of FIG. 30, the difference D between the density data of the pixel showing the maximum density and the value of the pixel showing the minimum density data among the three adjacent pixels. However, if it is larger than the second predetermined value D _TH , the density data transfer processing is not performed as in the previous embodiment. The reason for this is the same as in the previous embodiment, in order to prevent the possibility of relocation of an edge to a character image.

Returning to the flowchart of FIG. 28, the third embodiment of the present invention will be described. The processing of steps S701 to S704 is the same as the processing of steps S501 to S504 of the first embodiment. Since it is the same, the description here will not be repeated.

In step S705, of the pixel data stored in the first memory 250, the (window number × 3) -th pixel data is read out and stored in the image data L.

In this embodiment, the window numbers correspond to every three adjacent pixels, and are different from the window numbers corresponding to every two adjacent pixels in the first embodiment. is there.

Next, in step S706, the image data M
Then, from the first memory 250, (window number × 3 +
1) Read and store the data of the pixel. Similarly, in step S707, the image data R is stored in the first memory 25
From 0, the data of the (window number × 3 + 2) th pixel is read and stored. Next, in step S708, the three average values of the image data L, M, and R are compared with the maximum value (first predetermined value) 255 of the density data.
If it is less than or equal to 255, the process proceeds to the next step S709, and if it is greater than 255, the process proceeds to step S720 without performing the line screen processing. Next, in step S709, of the data stored in the image data L, M, and R, the largest one is set to data A. Similarly, in step S710, 3
The smallest one of the two data is data B. Then, in step S711, the difference between the data A and the data B is calculated. In step S712, it is determined whether or not the difference is less than the second predetermined value D _TH shown in FIG. When the difference is less than the predetermined value D _TH is to perform the relocation process of the density data shown in (1) in FIG. 30, the process proceeds to step S713 following flow, when the difference is not less than the predetermined value D _TH Does not transfer the density data, as shown in (2) of FIG. 30, the flow proceeds to step S720. In step S720, the values of the image data L, M, and R are output as they are, and stored in the second memory 251. Then, in step S721,
After the window number is incremented in order to perform the process for the next window, the process returns to the flow step S704.

On the other hand, in step S611, the difference is determined to be a predetermined value D.
_If it is less than _TH , in step S713, a value obtained by adding all the values of the image data L, the image data M, and the image data R to the image data M is stored. Then, in step S714, the image data M becomes the maximum value, that is, 255.
It is determined whether it is greater than. If the image data M does not exceed the maximum value, a value of 0 is stored in the image data L in step S718, and the image data R is stored in step S719.
After the value of 0 is stored in the subroutine, the flow proceeds to step S720.

On the other hand, in step S714, the image data M
Is greater than the maximum value 255, step S71
In step 5, half the value of the value obtained by subtracting the maximum value 255 from the image data M is stored in the image data L. In step S716, a value obtained by subtracting the maximum value 255 and the image data L from the image data M is stored in the image data R. In step S717, the maximum value 255 is stored in the image data M. That is, from step S715 to step S7
If the value obtained by adding the density data of the three adjacent pixels exceeds the maximum value 255 by the processing in step 17,
The half of the value that is exceeded is evenly distributed to the left and right image data L and R.

In this way, the values of the image data L, M and R are determined, and the values are output to the second memory 251 and stored in step S720. Then, in step S721, after the window number is incremented in order to process the pixel corresponding to the next window, the flow proceeds to step S704, and thereafter, the same processing as described above is performed.

FIG. 31 is an image formed by the above-described third embodiment of the present invention with respect to the original image shown in FIG.

FIG. 33 is a diagram showing a system configuration around a line screen processor according to a fourth embodiment of the present invention.

Referring to the figure, the configuration of the system is basically the same as that of the first embodiment shown in FIG. 5, except that a movement amount reference table 253 is provided. As will be described below, the moving amount reference table determines the moving amount of the density data in the line screen processing according to the difference between the density data of two adjacent pixels. The contents are specifically shown in FIG. In FIG. 34, the horizontal axis represents the difference obtained by inputting the difference between the density data, and the vertical axis represents the relocation amount corresponding to the difference as the output.

FIG. 35 is a schematic diagram showing the procedure of processing density data for each pixel in the fourth embodiment.

FIG. 35A shows the basic concept of processing the density data of this embodiment. In the figure, the vertical axis indicates the density level of 256 gradations (0 to 255), and the horizontal axis indicates the left density L and right density data R of a window. In this example, the left density data L
Greater density value of, D _LR than the density value of the right density data R
Only the difference has occurred. The density data transfer amount X corresponding to the difference _DLR is equal to the line screen processor 204.
Is obtained by accessing the data in the reference table 253, and the value of the density data R on the right is
The data is transferred to the left density data L as indicated by a broken line. In this example, as a result, the value of the left density data L increases to the position indicated by the broken line, and the value of the right density data R becomes 0.

In the case (2) of FIG. 10, the processing is shown in the case where the difference _DLR between the left density data and the right density data is large. In this case, the transfer of the density data as shown in (1) of FIG. 10 is not performed. The reason why the relocation is not performed is that, for example, in the case of an image such as character data in which an edge portion is clearly shown, if the relocation is performed as shown in FIG. 10A, the position of the edge portion moves. This is because the reproducibility of the image is not preferable. The transfer amount X corresponding to the difference D _LR in this case is set to “0” on the transfer amount reference table as shown in FIG.

FIG. 10C shows another example of the transfer of image data. In this example, since the difference _DLR between the left density data L and the right density data R is small, the density data is basically transferred as shown in (1). However, in this example, since the value of the left density data L is large, if all the values of the transfer amount X shown in the transfer amount reference table of FIG. 34 are transferred as they are, the density level exceeds the maximum value 255 of the density level. In this case, the transfer amount X 'is determined as indicated by a broken line so that the upper limit of the left density data L becomes the maximum value 255. Therefore, as a result of the relocation, the value of the left density data L becomes the maximum value 255, and the right density data R
Does not become 0, and remains as density data at the position indicated by the broken line. By doing so, the amount of toner attached to the pixel corresponding to the left density data L becomes the maximum value, and the density level of the entire pixel constituting this window is maintained.

Next, the flowcharts of FIGS. 36 and 37 according to the fourth embodiment will be described. Note that the processing of steps S801 to S807 is the same as that of steps S501 to S507 of FIG. 7 in the first embodiment.
Since the processing is the same as described above, the description here will not be repeated.

Based on the difference obtained in step S807, in step S808, the relocation amount X for the corresponding difference is selected from the relocation amount reference table 253 in FIG. Then, in step S809, the smallest one of the three values of the transfer amount X, the image data R, and the (maximum value−image data L) is determined, and the process proceeds to the following steps.

The reason why such a judgment process is performed is that it is necessary to obtain a value which can be actually transferred between adjacent pixels. That is, if the transfer amount X determined by the difference between the two pixels is smaller than the value (image data R) on the transfer side, the processing may be performed using the transfer amount X as it is, but if the transfer amount X is larger. The image data R becomes negative in processing, and as a result, the entire density cannot be maintained.

Further, if the relocated side (image data L) is relocated beyond its maximum value, the adjacent 2
The density of the entire pixel cannot be maintained. As described above, the processes of steps S810 and 811 are performed in order to set the smallest value determined in step S809 as the actual relocation amount.

Then, in step S812, the image data L
Is stored with a value obtained by adding the image data L and the transfer amount, and in step S813, a value obtained by subtracting the transfer amount from the image data R is stored in the image data R. Image data L and R determined in steps S812 and S813
Is output to and stored in the second memory 251 in step S814, and after the window number is incremented in step S815, the flow returns to step S804 in the same manner as in the first embodiment.

FIG. 38 is a diagram showing the relationship between the original density and the print density used for controlling the tone of a halftone image in printing for explaining the features of the fifth embodiment of the present invention.

Referring to the figure, curves corresponding to various tone reproduction characteristics are drawn. In this embodiment, the standard tone reproduction data shown in FIG. 38 is input from the image reader IR or an external device. The output data of the image is corrected using the offset value corresponding to the preset tone curve using the tone designation switch 221 of the operation unit 218 in FIG. 39, and then the line screen processing is performed. The offset value for each curve is stored in the offset value reference table 254 in FIG.

FIG. 41 is a diagram for explaining how to obtain an offset value in this case by taking a highlight emphasis curve as an example from the tone reproduction characteristics of FIG.

Referring to the drawing, it is assumed that the average density of two adjacent pixels is x as input data. In this case, the difference between the point A of the highlight emphasis curve corresponding to the input data x and the point B 'of the standard tone reproduction line is the offset value V. According to the gradation characteristics of the highlight emphasis curve, the offset value is a positive value as is apparent from the figure.

FIG. 42 is a diagram showing a document subjected to image processing according to the fifth embodiment of the present invention. FIG. 42 shows an example of tone control by highlight emphasis corresponding to FIG.

It is assumed that density data of two adjacent pixels as shown in (1) of FIG. 42 has been obtained from the image reader IR, and the average value is x. Then, the offset value V obtained as shown in FIG. 41 is added to the density data of each pixel as shown in (2) of FIG. The line data screen processing described in the first embodiment is performed on the density data subjected to offset correction in highlight emphasis as shown in FIG. 42 (3).

FIGS. 43 and 44 are flow charts for explaining the operation of the line screen processor according to the fifth embodiment of the present invention.

Referring to the figure, steps S901 to S908 are the same as the contents of steps S501 to S508 of the first embodiment, and therefore description thereof will not be repeated.

If the difference is less than the predetermined value in step S908, it is determined in step S909 whether the tone setting switch 221 has been used to input a tone setting.

If there is no tone setting input, tone control is not necessary, and the flow proceeds to step S915.
Then, the same processing as in the first embodiment is performed.

On the other hand, if there is a tone setting input, an offset table corresponding to the tone setting content is prepared from the offset value reference table 254 in step S910. Next, the average density data Da of the image data L and R
Is calculated (S911). An offset value Do is obtained from the offset table based on the data Da (S912).

When the offset value Do is obtained, step S9 is performed.
13, the offset value Do is assigned to each of the image data L and R.
Are obtained as image data L 'and R' (S913). Then, the image data L is converted to image data L '.
And R ′ are added, and the flow is step S
Proceed to 916.

The contents of steps S916 to S921 are the same as those of steps S510 to S921 of the first embodiment.
515, the description is not repeated here.

FIG. 45 is an image in which tone control by highlight emphasis according to the fifth embodiment is performed, in which the image of FIG. 16 is compared with that reproduced by the standard tone reproduction, and FIG. 46 is a fifth embodiment. 7 is an image when tone control is performed by shadow emphasis.

In the fifth embodiment, the adjacent two
Although the present invention is applied to the line screen processing for pixels, the present invention can be similarly applied to the line screen processing for three adjacent pixels shown in the second embodiment.

[0109]

As described above, according to the present invention, data is processed so that a part or all of the received predetermined image data is transferred to the image data of the adjacent pixels. The continuity is ensured, and the graininess of the halftone portion is improved while maintaining the resolution.
It can also prevent the position of the edge part from moving.
You.

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a digital copying machine main body according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration of an optical system in the optical unit 2 shown in FIG.

FIG. 3 is a block diagram showing a configuration of an entire system of the digital copying machine shown in FIG. 1;

FIG. 4 is a flowchart showing a main routine of the digital copying machine shown in FIG. 1;

FIG. 5 is a system block diagram showing a configuration around a line screen processor of FIG. 3;

FIG. 6 is a part of a flowchart showing control contents of the line screen processor of FIG. 5;

FIG. 7 is another part of the flowchart showing the control contents of the line screen processing processor of FIG. 5;

FIG. 8 is a diagram showing a change of a main scanning effective area signal and a sub-scanning effective area signal for a document according to the first embodiment of the present invention.

FIG. 9 is a diagram showing a relationship among a main scanning effective area signal, pixel data, and a window number according to the first embodiment of the present invention.

FIG. 10 is a schematic diagram showing a data processing procedure by transferring density data in adjacent pixels according to the first embodiment of the present invention.

FIG. 11 is a diagram showing a state in which density data transfer processing has been performed for each pixel according to the first embodiment of the present invention, in relation to a window number and a line number.

FIG. 12 is a diagram showing a granularity evaluation of an image to which the first embodiment of the present invention is applied, in consideration of visual characteristics.

FIG. 13 is a diagram showing a granularity evaluation of an image based on a conventional intensity modulation method in consideration of a visual characteristic with respect to FIG.

FIG. 14 is a diagram showing visual MTF characteristics shown for performing the evaluations of FIGS. 12 and 13;

FIG. 15 is an original image read by the digital copying machine according to the first embodiment of the present invention.

FIG. 16 is an image formed by the first embodiment of the present invention with respect to the original image shown in FIG.

FIG. 17 is a diagram showing a character document read by the digital copying machine according to the first embodiment of the present invention.

18 is an image obtained when the first embodiment of the present invention is applied to the original image shown in FIG. 17, and is an image obtained when the screen direction is set in the horizontal direction with respect to the drawing. .

19 is an image obtained when the first embodiment of the present invention is applied to the original image shown in FIG. 17, and is an image obtained when the screen direction is set to be up and down with respect to the drawing. .

FIG. 20 is an image generated by the conventional dither method for the document shown in FIG. 17;

FIG. 21 is another modified example according to the first embodiment of the present invention, in which the transfer state of the density data is set to 45 in the screen direction.
FIG. 9 is a diagram showing a relationship between a window number and a line number when the degrees are set to degrees.

FIG. 22 is a diagram showing still another modified example of the first embodiment of the present invention, in which the transfer state of density data is shown by a relationship between a window number and a line number when the screen direction is set to 26.6 degrees. FIG.

FIG. 23 corresponds to a modification of FIG. 21 and is an image when the screen direction is set to 45 degrees.

FIG. 24 corresponds to the modification of FIG. 22 and is an image when the screen direction is set to 26.6 degrees.

FIG. 25 is a part of a flowchart showing the control contents of the line screen processor according to the second embodiment of the present invention;

FIG. 26 is another part of the flowchart showing the control contents of the line screen processing processor according to the second embodiment of the present invention.

FIG. 27 is a diagram showing an outline of density data transfer processing for three adjacent pixels according to the second embodiment of the present invention.

FIG. 28 is a part of a flowchart showing the control contents of the line screen processor according to the third embodiment of the present invention;

FIG. 29 is another part of the flowchart showing the control contents of the line screen processor according to the third embodiment of the present invention.

FIG. 30 is a diagram showing an outline of density data migration processing for three adjacent pixels according to the third embodiment of the present invention.

FIG. 31 is an image formed by the third embodiment of the present invention with respect to the original image shown in FIG.

FIG. 32 is a block diagram showing a configuration of an entire system of a digital copying machine as a modification of the first and second embodiments of the present invention.

FIG. 33 is a system configuration diagram around a line screen processing processor according to a fourth embodiment of the present invention.

FIG. 34 is a diagram showing the contents of a movement amount reference table used in the fourth embodiment of the present invention.

FIG. 35 is a schematic diagram showing a procedure for processing density data for each pixel according to the fourth embodiment of the present invention.

FIG. 36 is a part of a flowchart showing the control contents of the line screen processor according to the fourth embodiment of the present invention;

FIG. 37 is another part of the flowchart showing the control contents of the line screen processor according to the fourth embodiment of the present invention;

FIG. 38 is a diagram showing the relationship between the document density and the print density shown for explaining the features of the fifth embodiment of the present invention.

FIG. 39 is a block diagram showing an overall configuration of a digital copying machine according to a fifth embodiment of the present invention.

FIG. 40 is a system block diagram showing a configuration around a line screen processor according to a fifth embodiment of the present invention.

FIG. 41 is a diagram for explaining how to obtain an offset value in the tone reproduction characteristics of FIG. 38, taking highlight emphasis as an example.

FIG. 42 is a diagram showing the principle of image processing using highlight emphasis as an example according to the fifth embodiment of the present invention.

FIG. 43 is a part of a flowchart showing the control contents of the line screen processor according to the fifth embodiment of the present invention;

FIG. 44 is another part of the flowchart showing the control contents of the line screen processor according to the fifth embodiment of the present invention;

FIG. 45 is an image obtained when tone control is performed by highlight emphasis according to the fifth embodiment of the present invention.

FIG. 46 is an image when tone control is performed by shadow enhancement according to the fifth embodiment of the present invention.

[Explanation of symbols]

 204 line screen processing processor 250 first memory 251 second memory 252 timing control unit In the drawings, the same reference numerals indicate the same or corresponding parts.

Continuation of the front page (56) References JP-A-3-217168 (JP, A) JP-A-4-200075 (JP, A) JP-A-3-143167 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) H04N 1/40-1/409 B41J 2/52

Claims (3)

(57) [Claims] And receiving means according to claim 1] receives the image data read for each pixel, a data processing means for processing to relocate the image data of pixels adjacent to some or all of the predetermined image data received, the adjacent To calculate the difference in image data between pixels
Calculating means for calculating the difference when the calculated difference is smaller than a predetermined threshold value.
While outputting image data processed by the data processing means ,
If the difference is greater than a predetermined threshold, the data processing
A data output means for outputting image data without processing in a step . 2. The image processing apparatus according to claim 1, wherein the data processing unit transfers the image data of one adjacent pixel to the image data of another pixel based on a value determined according to a difference between the image data of the adjacent pixels. Item 2. The image processing apparatus according to Item 1. 3. A receiving means for receiving image data read for each pixel, and processing the received image data so that image data of one pixel in adjacent pixels is transferred to image data of the other pixel. Data processing means for outputting processed image data; and image data when the difference between the image data of the one pixel and the image data of the other pixel is equal to or greater than a first predetermined value. A first control means for controlling the data processing means so as not to perform the processing of, when a difference between the image data of the one pixel and the image data of the other pixel is less than the first predetermined value, A second predetermined value determined by the average value of the image data of the adjacent pixel is added to or subtracted from the image data of each pixel constituting the adjacent pixel, and the second predetermined value is changed by the second predetermined value. Image processing apparatus including a second control means for controlling said data processing means to process the image data as image data received above the.