JPH08228298A - Method and device for processing image - Google Patents

Abstract

PURPOSE: To provide an image processing method and device forming an image with high image quality by preventing the occurrence of so called void in the image forming adopting the electro-photographic system. CONSTITUTION: A density adjustment circuit adjusts the density along a line width of each line segment forming a formed image (e.g. character 'A'). That is, (1) when the line width is less than 100μm, the density is not adjusted, (2) when the line width is 100μm or over and less than 1mm, the density of the edge of the line is increased and the density in the inside is decreased, or (3) when the line width is less than 1mm, the density in the vicinity of the edge of the line is decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and an apparatus thereof, and more particularly to an image processing method and an apparatus thereof for connecting a computer for generating image data and a printer for outputting an image.

[0002]

2. Description of the Related Art When a printer for forming and outputting an image according to a conventional electrophotographic method is connected to a host computer to output an image, there are some cases where the image quality of the output image is deteriorated due to the characteristics of the printer. . For example, a digital full-color copying machine using an electrophotographic method is used as a color printer, and image data transmitted from a host computer in which four colors (cyan, magenta, yellow, and black) are superposed on each other is used as it is. When toner is used to form an image on the same area of the recording medium,
As shown in FIG. 9, the toner layer becomes thicker than necessary, and the toner that could not be adhered scatters to the outside of the area where the image should be originally formed (the peripheral area of the image), degrading the image quality. The toner scattering phenomenon sometimes occurred.

Further, in the case of an image (solid image) drawn with a relatively thin solid line having a width of about 1 mm or less, the toner is normally transferred to the edge portion of the image on the recording medium,
As shown in FIG. 10, the toner is not normally transferred to the portion sandwiched by the two edges. For example, when the recording medium is a white recording paper, the formed image is partially removed in white, that is, a so-called hollow phenomenon. May occur.

For such deterioration of image quality, when a corresponding image is transmitted from the host computer, the image processing unit of the printer apparatus is adapted to the characteristics and performance of the printer engine which is an image forming unit to some extent. The image information is transferred to the image forming unit after the image is converted into the image. For example, the toner scattering phenomenon is likely to occur when the toner layers are overlapped more than necessary. Therefore, in the image processing unit, the chromaticity of each color is different for image information in which toner is overlaid on the same portion of the recording medium. Processing is performed to reduce the amount of toner of each color to such an extent that it does not pose a problem in practice.

As shown in FIG. 11, for example, in an image in which the color components are cyan, magenta, and yellow, the same amount is thinned out from each color component, and that amount is replaced by black toner (UCR (lower Color removal: Under
It is executed by a process called Color Removal).

[0006]

However, the UCR processing of the above-mentioned conventional example has an excellent effect on the toner scattering phenomenon, which is commonly seen in color images, but it does not affect the hollow phenomenon of solid images. There is a problem that a sufficient effect cannot be obtained, and particularly this phenomenon occurs frequently in an electrophotographic printer that handles a binary image.

The present invention has been made in view of the above-mentioned conventional example, and an object of the present invention is to provide an image processing method and apparatus capable of preventing a hollow image phenomenon and obtaining a high-quality image.

[0008]

In order to achieve the above object, the image processing method of the present invention comprises the following steps. That is, an image processing method of receiving image information from a host computer, performing image processing, forming an image, and outputting an image, which is based on a receiving step of receiving the image information, and based on the received image information. According to the determination step of determining the width of the line forming the image and the determination result,
An image processing method comprising: an adjustment step of adjusting each pixel value obtained from the received image information so as to be changed; and an image forming output step of forming an image according to the adjustment result and outputting the image. .

According to another aspect of the invention, there is provided an image processing apparatus for receiving image information from a host computer, performing image processing, forming an image, and outputting an image, the receiving means receiving the image information. A discriminating means for discriminating the width of a line forming an image based on the received image information;
According to the determination result, the image forming apparatus further comprises an adjusting unit that adjusts each pixel value obtained from the received image information so as to be changed, and an image forming output unit that forms an image according to the adjusting result and outputs the image. An image processing device is provided.

[0010]

With the above construction, the present invention receives the image information from the host computer, determines the width of the line forming the image based on the received image information, and obtains it from the received image information according to the result of the determination. Each pixel value is adjusted so as to be changed, an image is formed according to the adjustment result, and an image is output.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a side sectional view showing the structure of a color copying machine which is a typical embodiment of the present invention. FIG.
In the figure, 201 is an image scanner unit, and 400
Scan the original at a resolution of dpi (dots / inch),
This is the part that performs digital signal processing. A printer unit 202 is a unit that prints out an image corresponding to the original image read by the image scanner 201 in full color on paper at a resolution of 400 dpi.

In the image scanner unit 201, 20
Reference numeral 0 is a mirror surface pressure plate, which is a platen glass 203.
The upper original 204 is illuminated by the lamp 205, and the mirror 2
06, 207, 208, a lens 209 forms an image on a 3-line sensor (CCD) 210, and sends it to the signal processing unit 211 as full color information red (R), green (G), and blue (B) components. To be In addition,
The carriage 227 fixing the 205 and 206 is at a speed v, and the carriages 207 and 208 are at a speed of 1/2 v, and mechanically moves in a direction perpendicular to the electric scanning (main scanning) direction of the line sensor, thereby the entire surface of the original Is scanned (sub-scanning).

In the signal processing section 211, the read multi-valued image signal is electrically processed, and magenta (M),
The printer unit 20 is decomposed into cyan (C), yellow (Y), and black (Bk) components and subjected to image processing described later.
Send to 2. In addition, one component of M, C, Y, and Bk is sent to the printer unit 202 for each document scanning by the image scanner 201, and one printout is completed by a total of four document scanning.

The M, C, Y, and Bk image signals sent from the image scanner unit 201 are supplied to the laser driver 2.
Sent to 12. The laser driver 212 modulates and drives the semiconductor laser 213 according to the sent image signal. The laser light scans the photosensitive drum 217 via the polygon mirror 214, the f-θ lens 215, and the mirror 216. Reference numeral 218 denotes a rotary developing device, which is a magenta developing unit 2
19, a cyan developing unit 220, a yellow developing unit 221, and a black developing unit 222, and four developing units alternately contact the photosensitive drum 217 to develop the electrostatic development formed on the photosensitive drum with toner. Reference numeral 223 denotes a transfer drum, which winds the paper supplied from the paper cassette 224 or 225 around the transfer drum 223, and transfers the image developed on the photosensitive drum to the paper.

In this way, after the four colors M, C, Y and Bk are sequentially transferred, the paper passes through the fixing unit 226, the toner is fixed on the paper, and then the paper is ejected. The color copying machine according to the present embodiment has not only a copy function for a document but also color image data output from a computer,
It has a function to output the color image on copy paper. In FIG. 1, reference numeral 232 is a computer interface (I / F), and color image data (RGB) from a computer (not shown) connected to this color copying machine.
(Represented by components) and input to the signal processing unit 211. The received data has a data format represented by vector information used in general PDL, not a data format such as only a bitmap, and fonts stored in a ROM or a hard disk described later. It is developed into a dot pattern using data and the like.

Reference numeral 231 denotes an operation panel, which is used for copying a document, switching image input sources, and LUT (L
Switch operation of ook up table). [Image Scanner Unit (FIG. 2)] FIG. 2 is a block diagram showing the arrangement of the image scanner unit 201. In FIG. 2, 210-1, 210-2 and 210-3 are respectively
A CCD (solid-state image sensor) line sensor having red (R), green (G), and blue (B) spectral sensitivity characteristics, each of which has 8 bits (0 to 25) after A / D conversion.
The signal of 5) is output.

Since the CCD line sensors 210-1, 210-2, 210-3 used in this embodiment are arranged with a constant distance, the spatial shifts of the delay elements 401 and 402 are corrected. It 40
Reference numerals 3, 404 and 405 denote log converters (luminance density conversion circuits) that convert the input luminance signal (RGB signal) into a density signal (YMC signal). Reference numeral 406 denotes a masking UCR (undercolor removal) process from the YMC signal to convert it into magenta (M '), cyan (C'), yellow (Y '), and black (Bk') signals and read each signal. Is a masking UCR (under color removal) circuit that outputs a frame-sequentially with a predetermined bit length (8 bits in this embodiment). The conversion relationship between Y, M, C, and Bk and Y ', M', C ', and Bk' is as follows.

Y ′ = Y−α · min (Y, M, C) M ′ = M−α · min (Y, M, C) C ′ = C−α · min (Y, M, C) Bk ′ = Bk = min (Y, M, C) Here, 0 <α ≦ 1, where α is a coefficient indicating the degree of UCR processing. This conversion relationship is stored in the LUTROM 409 as a lookup table (hereinafter referred to as LUT). In actual UCR processing), this LU
With reference to T, the YMC signal is converted into a Y'M'C'Bk 'signal. A plurality of LUTs are stored in the LUTROM 409, and they can be appropriately switched and used according to the color tone of the input image.

Reference numeral 407 is a known spatial filter circuit,
Performs edge correction and other processing. A density adjustment circuit 410 adjusts the density value according to the line width on which an image is formed. This density adjustment will be described later in detail. On the other hand, 414 is a microcomputer (hereinafter, CPU) that controls the present apparatus, 415 is a ROM that stores programs for operating the CPU 414, and 416 is RAM that is used as a work area for executing various programs. 413 is an input / output port (hereinafter referred to as I / O port) connected to the CPU 414, and 417 is a font R that stores an outline font that can be easily processed such as scaling.
OM (FROM).

Now, this apparatus is equipped with a platen glass 2
A copy of the original 204 placed on the printer 03 or by inputting color image data (RGB signals) output from a computer connected to the apparatus forms a color image and copies the image. To print out. Input data switching for that purpose is performed by the selector 408. The switching is performed by a command from the CPU 414 based on a command from the operation panel. Similarly, switching of the LUT is also performed by an instruction from the CPU 414 based on an instruction from the operation panel.

The following description is based on the premise that the apparatus of this embodiment inputs color image data as image information from the host computer and performs image processing. The color image data sent from the host computer is interpreted by the computer interface (I / F) 232, and the character data is converted into a bitmap by referring to the outline font data stored in the FROM 417, and is converted into a selector (SEL) 408. Is output. In addition, graphic data represented by vector data and image data such as natural images can also be displayed on a computer interface (I / I).
F) 232 produces dot data, and the selector (S
EL) 408.

On the other hand, a computer interface (I /
F) 232 notifies the CPU 414 of the image output position of the character image or line drawing, the output position of each vector of the outline font data, etc., based on the image information sent from the host computer. Based on these pieces of information, the CPU 414 instructs the density adjusting circuit 410 which part of the image data the density should be adjusted. Then, the density adjustment circuit 410 determines the width of the lines forming the image of the character or line drawing, and performs the density adjustment as described below according to the width.

Next, the operation of the density adjusting circuit 410 will be described in detail with reference to FIG. Here, FIG.
The character image "A" formed by the apparatus of the present embodiment as shown in FIG. 3B is a toner amount distribution diagram of the cross section of the character image "A" taken along the line aa 'shown in FIG. In order to simplify the description, first, the case where an image is formed with a single color toner (for example, black toner) will be described.

As shown in FIG. 3B, in such a character image, the amount of toner in the edge portion is generally larger than that in the inner portion even if the density values are the same, and a hollow phenomenon is likely to occur. This is because the toner layer is compressed when the toner image is transferred from the photosensitive drum 217 to a recording sheet that is a transfer material.
At the edge portion, the pressure is dispersed to the outside, but at the inner portion, the pressure is not dispersed and is compressed.
It occurs because it is difficult to separate from.

The density adjusting unit 410 of the present embodiment is used for a binary image having a high contrast such as a character image as shown in FIG.
In an image having edges at both ends as shown in (b), the density value of the edge part is increased, while the density value of the inner part is decreased. As a result, the amount of toner at the edge portion becomes large during actual image formation, and the amount of toner at the inner portion is reduced.

The line width of a line image such as a character image is
The minimum range is 1 pixel, which is the maximum resolution of the apparatus, and the maximum range is the entire width of the recording paper. In a line image having a sufficiently wide area or a wide width, the compression pressure of the toner is unlikely to be locally increased, and thus the hollow defect is generally unlikely to occur. Therefore, in this embodiment, the image processing method is changed according to the width of the line image.

Specifically, the line width is (1) 100 μm.
Less than (2) 100 μm or more, less than 1 mm, (3) 1 m
The processing method is changed for images of m or more.
In the case of an image having a line width of 100 μm or less like the cross section along the line segment bb ′ in FIG. 4A, it is difficult to distinguish the edge portion and the inner portion from the resolution of the printer. Further, in the case of such a thin line, there is no difference in the pressure distribution per cross section to the extent that the entire line can be regarded as one edge. Therefore, in the case of a line image having a line width of 100 μm or less, it is not necessary to change the toner amount as shown in FIG.

Next, as in the case of the cross section along the line cc 'in FIG. 4A, when the hollowing-out phenomenon is most likely to occur in the line width range of 100 μm to 1 mm, FIG. As shown in (c), the toner amount in the edge portion is large, and the toner amount in the inner portion is small. In the density adjusting circuit 410, the density of the edge portion is increased, while the image processing is performed to decrease the density of the inner portion. To do. In this case, the length of the edge portion needs to be changed according to the characteristics of the printer portion, but in the case of a printer having a resolution of 400 dpi as in this embodiment, one pixel (about 63.5 μm) to two pixels It has been experimentally confirmed that the hollowing-out can be prevented by setting the degree to a certain degree.

Further, if the line width is 1 mm or more, the hollow phenomenon generally does not easily occur, but as shown in FIG. 6 (a), the hollow phenomenon may occur near the edge portion. Therefore, in this case, as shown in FIG. 6B, the density adjusting circuit 41 is arranged so that the toner amount becomes small near the edge portion.
At 0, image processing is performed so as to reduce the density near the edge portion. By performing such image processing, it is possible to prevent the hollow image phenomenon near the edge portion.

The above-mentioned processing is performed by partially changing the density value of the density data developed in the page memory (not shown) provided in the density adjusting circuit 410 based on the instruction from the CPU 414. Done. Although the above description has been made on the case of forming an image using a single color toner, the case of forming an image using a plurality of toners (that is, the image information transmitted from the host computer is two or three).
(Or four color components), even if the line image has the same line width, for example, when the image formation with a single color toner and the image formation by superposing two color toners are performed, the toner amount is increased. However, it is necessary to change the process even if the line width is the same.

Hereinafter, the case of forming an image using two toners will be described with reference to the distribution of each toner shown in FIG. Also in this figure, consider the character image “A” shown in FIGS. 4A and 5A as an example.
That is, even if the line width is narrow (for example, 100 μm or less), the toner layer becomes thick, and therefore, as shown in FIG. 6A, the density value of the color component corresponding to each toner is reduced to reduce the toner The amount is reduced so that the pressure due to toner compression does not exceed a certain level. Next, when the line width is about 100 μm to 1 mm,
As shown in (b), the density value of each color component is adjusted so that the total toner amount is reduced and the toner amount is increased at the edge portion, while the toner amount is reduced at the inner portion. Further, in the case where the line width is 1 mm or more, FIG.
The image processing is performed such that the toner amount is reduced as a whole and the density value near the edge is reduced so that the toner amount near the edge is reduced.

Therefore, according to the present embodiment, by changing the density values of the edge part and the inner part according to the width of the line drawing, or by changing the density values in the vicinity of the edge part, a plurality of values can be further obtained. In the case of forming an image using toner, the toner amount can be adjusted by reducing the total toner amount, so that it is possible to prevent a hollow defect in the formed image and obtain an image of high quality.

Although the apparatus used in this embodiment was a full-color copier / printer capable of inputting multi-valued image data and performing image processing, the present invention is not limited to this. For example, a printer that cannot express gradation can be used. In a full-color printer, it is possible to change the amount of toner in pixel units, but in a binary printer that cannot express gradation, it is only possible to place a toner transfer material on a pixel unit basis. Perform such processing.

FIG. 7 is a diagram showing toner amount adjustment when a binary printer is used as the image output device. even here,
As shown in FIG. 7A, the character image "A" is taken as an example, and the toner distribution in the cross section along the line d-d 'is considered.
In this case, as shown in FIG. 7B, the toner is placed on the transfer material at some pixels in the edge portion, and the toner is not placed on the transfer material for one pixel near the edge portion. Image processing is performed on the inner side portion thereof so that the toner is placed on the transfer material. That is, for each color component, the image data value is processed to "1" when the toner is placed on the transfer material, and to "0" when the toner is not placed.

In this case, it is not necessary to limit the number of pixels in the vicinity of the edge portion where the toner is not placed on the transfer material to one pixel. For example, the line d of the same character image "A" as shown in FIG. Considering the cross section along −d ′, it is possible to further increase the pixel interval in which the toner is not placed on the transfer material as shown in FIG. 8B, for example, two pixels.

In this way, the pressure due to toner compression is released toward the toner-free area of one pixel,
It is possible to prevent the hollow phenomenon in the inner part. In particular, by widening the pixel interval in which toner is not placed on the transfer material, in the case of a binary printer, the effect of line width is small, but it is possible to prevent the hollow dot phenomenon that tends to occur when multicolor toners are stacked. it can. In the case of a binary printer, this processing is particularly effective because it is not possible to gradually reduce the toner amount in pixel units.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0038]

As described above, according to the present invention, the image information from the host computer is received, the width of the line forming the image is discriminated based on the received image information, and according to the discrimination result, Adjustment is performed so as to change each pixel value obtained from the received image information, image formation is performed according to the adjustment result, and the image is output. Therefore, the pixel value is corrected according to the line width of the image. There is an effect that it can be prevented and a high quality image can be output.

In particular, according to the third aspect of the invention, the density is adjusted by increasing the density value of the edge portion or decreasing the density value inside thereof according to the line width. With the adjusted image data, it is possible to prevent the hollow image phenomenon from occurring in the image formed. Further, according to the invention described in claim 6, when the binary image processing is handled, a blank pixel is provided by setting the value for each certain pixel to "0", so that the hollow image phenomenon does not occur in the formed image. To be suppressed.

[Brief description of drawings]

FIG. 1 is a side sectional view showing the configuration of a color copying machine that is a typical embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an image scanner unit 201.

FIG. 3 is a diagram showing an image (“A”) formed by the apparatus shown in FIG. 1 and toner distribution in a cross section taken along line aa ′.

FIG. 4 is a diagram showing an image (“A”) formed by the apparatus shown in FIG. 1, a toner distribution in a section along line aa ′, and a toner distribution in a section along line bb ′. Is.

5 is a diagram showing an image (“A”) formed by the apparatus shown in FIG. 1 and a toner distribution in a cross section of a portion where the line width of the image is large.

FIG. 6 is a diagram showing a cross-sectional toner distribution when forming a multicolor image.

FIG. 7 is a diagram showing an image (“A”) formed by a binary printer and a toner distribution in a cross section taken along a line d-d ′.

FIG. 8 is a diagram showing another example of an image (“A”) formed by a binary printer and a toner distribution in a cross section taken along a line d-d ′.

FIG. 9 is a diagram showing a toner scattering phenomenon.

FIG. 10 is a diagram showing a toner dropout phenomenon.

FIG. 11 is a diagram illustrating UCR processing.

[Explanation of symbols]

200 Mirror Surface Pressure Plate 201 Image Scanner Section 202 Printer Section 203 Original Plate Glass (Platen) 205 Lamps 206, 207, 208 Mirror 209 Lens 210 3 Line Sensor (CCD) 211 Signal Processing Section 212 Laser Driver 213 Semiconductor Laser 214 Polygon Mirror 215 f- θ lens 216 Mirror 217 Photosensitive drum 218 Rotating developing device 219 Magenta developing part 220 Cyan developing part 221 Yellow developing part 222 Black developing part 223 Transfer drums 224, 225 Paper cassette 226 Fixing unit 227 Carriage 231 Operation panel 232 Computer interface (I / F) ) 401, 402 delay element 403, 404, 405 log converter (luminance density conversion circuit) 406 masking UCR (removal of undercolor) Road 407 spatial filter circuit 408 a selector (SEL) 409 LUTROM 410 concentration adjusting circuit 414 CPU 415 ROM 416 RAM 417 font ROM (FROM)

Claims (9)

[Claims] 1. An image processing apparatus for receiving image information from a host computer, performing image processing, forming an image, and outputting an image, comprising: receiving means for receiving the image information; and the received image information. On the basis of the determination result, determination means for determining the width of the line forming the image, adjustment means for adjusting the pixel value obtained from the received image information according to the determination result, and image formation according to the adjustment result. An image processing apparatus comprising: an image forming and outputting unit for performing an image output. 2. The image processing apparatus according to claim 1, wherein each pixel value obtained from the received image information is a density value, and the adjusting unit changes the density value. 3. When the width of the line is less than a first threshold, the adjusting means does not change the density value, and the width of the line is greater than or equal to the first threshold and less than a second threshold. When the line width is equal to or larger than the second threshold value, the adjusting unit increases the density value of the edge portion of the line and decreases the density value inside the line. The image processing apparatus according to claim 2, wherein the density value near the edge of the line is reduced. 4. The first threshold value is 100 μm, and the second threshold value is 100 μm.
The image processing apparatus according to claim 3, wherein the threshold value is 1 mm. 5. The image processing according to claim 3, wherein when the density value is color data composed of a plurality of color components, the sum of the density values of the plurality of color components is further reduced. apparatus. 6. The pixel value obtained from the received image information is binary, and the adjusting means changes the binary “1” value to “0”. The image processing device according to item 1. 7. The image processing apparatus according to claim 1, wherein the image forming and outputting unit is a printer according to an electrophotographic system. 8. The printer is a full-color printer that forms an image with four color toners of yellow (Y), magenta (M), cyan (C), and black (B). The image processing device according to item 1. 9. An image processing method for receiving image information from a host computer, performing image processing, forming an image, and outputting an image, the receiving step including receiving the image information, and the received image information. A determination step of determining the width of a line forming an image based on the above, an adjustment step of adjusting so as to change each pixel value obtained from the received image information according to the determination result, and an image formation according to the adjustment result. And an image forming and outputting step for outputting an image.