JPH10336454A - Image data processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high image quality output by applying smoothing correction to an image such as characters requiring correction without having effect on density and gradation even with respect to multi-value image data having the density and gradation. SOLUTION: The processor is provided with an image discrimination section 12 that detects the density of each pixel of received multi-value image data, allows an image correction section 13 to apply smoothing correction to only the image data whose density is a reference value or over and provides an output of the other multi-value image data as they are, and with an image data output section 14 that synthesizes the multi-value image data outputted as they are with the image data corrected by the correction means 13 and provides an output of the synthesized data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus using digital image data such as an optical printer such as a laser printer, a digital copying machine, and a plain paper facsimile apparatus, or image data processing applied to an image display apparatus. The present invention relates to an apparatus, and particularly to an image quality improving process.

[0002]

2. Description of the Related Art In an image forming apparatus or an image display apparatus as described above, character image data obtained by converting character code data using font data or image image data read by an image scanner or the like is quantized. Binary or multi-valued data is developed in a bitmap (dot matrix) format in a video memory area on a memory (RAM), read out sequentially, sent to the image forming unit (engine) as video data, and printed on recording paper. Image formation or image display (display)
To display the image on the screen.

[0003] In this case, if an image to be formed is an analog image, it can be continuous in any direction. However, a digital bitmap image obtained by quantizing the image and developing it is stepwise in units of one dot in the direction orthogonal to the dot matrix. Since the direction can be changed only in the shape, the formed image is distorted. As a result, a step (jaggy) occurs in which a straight line or a smooth curve inclined in a direction orthogonal to the direction orthogonal to the dot matrix is formed in a stepwise manner, and characters and images (particularly, contours) are made the same as or desired from the original image. It was difficult to form the shape.

As an effective method for reducing such image distortion, there is a method of increasing the resolution of a bitmap image by reducing the dot size of a dot matrix and increasing the density. However, increasing the resolution significantly increases costs. For example, 300 × 3
If the resolution of the two-dimensional bitmap of 00 dpi is doubled, a bitmap of 600 × 600 dpi can be obtained, but it requires four times the memory capacity and four times the speed of data processing.

[0005] As another method for reducing image distortion, an interpolating technique is used to connect a stepped corner to form a continuous slope, or to average the brightness of adjacent dots to obtain an edge. According to this method, the step-like jaggy becomes smooth, but the fine shape is also removed, so that there is a problem that the contrast and the resolution are reduced.

Therefore, for example, US Pat. No. 4,544,9
As shown in No. 22, smoothing is performed by selectively adding or removing dots smaller than a standard dot width to a specific portion of a dot pattern developed in a bitmap shape. Techniques are being developed. Therefore, as a technique for detecting a specific portion of the dot pattern to be corrected, pattern recognition and template matching have been performed.

According to this method, it is possible to improve the image quality by reducing the line shape without deteriorating the contrast. However, pattern recognition or template matching processing is performed for all positions of an arbitrary bitmap image. Since each dot is corrected according to the result, there is a problem that the processing apparatus is very expensive and the processing time is long.

In order to solve such a problem, the present inventors have developed a new image data processing method and apparatus disclosed in Japanese Patent Laid-Open No. 5-207282. According to this image data processing method, data that needs to be stored in a memory in advance in order to correct jaggies of a contour line of image data expanded in a bitmap shape and to improve image quality is measured. It is possible to reduce the number of dots to a minimum, determine the dots of the image data that need to be corrected, and determine the correction data for the dots that need to be corrected in a very short time by a simple determination and calculation by a microprocessor or the like.

That is, this image data processing method recognizes the shape of the line segment at the boundary between the black dot area and the white dot area of the image data developed in a bitmap form, and recognizes each required dot. Replace the feature of the line segment shape with a plurality of bits of code information, determine whether or not the dot needs correction using at least a part of the code information,
For the dots determined to require correction, correction is performed according to the code information.

On the other hand, an image data processing apparatus for realizing this image data processing method includes a window for extracting data of each dot in a predetermined area centered on a dot to be subjected to image data developed in a bitmap shape. The line segment shape at the boundary between the black dot region and the white dot region of the image data is recognized based on the image data extracted through the window, and the characteristics of the line segment shape recognized for the target dot are recognized. A pattern recognizing means for generating a plurality of bits of code information representing a dot, a discriminating means for judging whether or not the dot needs to be corrected by using at least a part of the code information. The correction data stored in advance is read out for the dots, using the code information generated by the pattern recognition unit as an address. It was equipped with a correction data memory for output.

Here, the pattern recognizing means indicates whether the dot to be subjected to the pattern recognition is a black dot or a white dot, as the code information representing the characteristic of the line segment shape recognized for each required dot. Generates code information including a code, a code indicating the inclination direction of the line segment, and a code indicating the position of the dot to be coded indicating the degree of the inclination from the dot at the end of the horizontal or vertical continuous line segment Was to do.

[0012]

Any of such conventional image correction techniques detects an edge portion of binary image data and performs smoothing correction for eliminating a step (jaggy) due to the resolution of the printing apparatus. The purpose was. Therefore, by performing such image correction, X
A good correction effect can be obtained when outputting a drawing or the like having a large amount of line data such as CAD data printed by a -Y plotter, or for an edge portion of a character font.

However, since image detection is performed on a binary image, it is not possible to effectively perform correction processing on image data such as gray scale having a gradation at one dot. When the jaggy correction is performed, there is a problem that the density gradation is disturbed.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. Even when input image data is multi-valued image data having a density gradation, the present invention has an effect on the density gradation. It is another object of the present invention to perform appropriate smoothing correction on an image portion requiring correction of characters and the like so that a high-quality image output can be obtained.

[0015]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention performs smoothing correction for smoothing a step at a boundary between a black dot area and a white dot area of image data developed in a bitmap form. In an image data processing apparatus having an image correction unit, each pixel density of input multi-valued image data is detected, and only image data having a density equal to or higher than a reference value is corrected by the image correction unit, and other multi-valued An image discriminating unit for outputting image data as it is, and an image data output unit for synthesizing the multi-valued image data output as it is and the image data corrected by the correcting unit and outputting the combined image data are provided.

According to this image data processing apparatus, smoothing correction is performed on an image portion having high density gradation such as characters and lines in multi-valued image data to improve the image quality, and the density gradation is lower than the reference value. Since the halftone image data is not corrected, there is no effect that the density gradation is disturbed.

If a means for variably setting the reference value of the density in the image discriminating section is provided, the optimum reference value can be set according to the configuration of the image and the state of the density gradation. Further, the image correction unit outputs correction information data indicating whether or not correction has been performed for each pixel, and the image data output unit outputs the corrected image for the pixel corrected in accordance with the correction information data. It is preferable to output the input image data as it is for pixels for which correction has not been performed and pixels which are not to be corrected.

In this case, the image data output section compares the density gradation of the two pixels in a portion where the pixel of the corrected image data overlaps a pixel that has not been corrected or a pixel that is not to be corrected. By selecting and outputting a pixel having a higher density gradation, it is possible to prevent a problem that a halftone image portion appears to be whitened out by correction dots.

[0019]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 2 is a block diagram showing a configuration of a laser printer which is an image forming apparatus embodying the present invention. The laser printer 2 includes a controller 3, an engine driver 4, a printer engine 5, and an internal interface (hereinafter abbreviated as "internal I / F") 6.

The laser printer 2 receives the print data transferred from the host computer 1 and develops it into bitmap data in page units by the controller 3 to convert the data into video data as dot information for driving the laser. The image data is converted and sent to the engine driver 4 via the internal I / F 6, and the printer engine 5 is sequence-controlled to form a visible image on a sheet.

A dot correction section 7 which is an image data processing device according to the present invention is provided in the internal I / F 6 to perform dot correction on video data sent from the controller 3 to improve image quality. is there.

The controller 3 includes a main microcomputer (hereinafter referred to as “MPU”) 31 and its MPU.
A ROM 32 storing programs, constant data, character fonts, and the like required by 31, a RAM 33 for storing temporary data, dot patterns, and the like, an I / O 34 for controlling input / output of data, and an I / O 34 Via M
An operation panel 35 connected to the PU 31;
They are connected to each other by a data bus, an address bus, a control bus, and the like. Further, an internal I / F 6 including the host computer 1 and the dot correction unit 7 is also connected to the MPU 31 via the I / O 34.

The engine driver 4 has a sub microcomputer (hereinafter referred to as “CPU”) 41 and its CP.
ROM 42 storing programs and constant data required by U41, and RAM 4 storing temporary data
3 and an I / O 44 for controlling data input / output, and are connected to each other by a data bus, an address bus, a control bus, and the like.

The I / O 44 is connected to the internal I / F 6 to input video data from the controller 3 and the state of various switches on the operation panel 35, and to input an image clock (WC).
LK) and a status signal such as paper end are output to the controller 3. Further, the I / O 44 is connected to the writing unit 26 and the other sequence device group 27 constituting the printer engine 5, and is also connected to various sensors 28 including a synchronous sensor described later.

The controller 3 includes a host computer 1
Receives commands such as print commands and print data such as character data and image data, and edits them.
If it is a character code, it is converted into a dot pattern necessary for image writing by a character font stored in the ROM 32, and bitmap data of those characters and images (hereinafter collectively referred to as “images”) are stored in the video R in the RAM 33.
It is expanded in the AM area in page units.

When the image clock WCLK is input together with the ready signal from the engine driver 4, the controller 3 converts the bitmap data (dot pattern) developed in the video RAM area in the RAM 33 into video data synchronized with the image clock WCLK. , Internal I
Output to the engine driver 4 via / F6. The dot correction according to the present invention is performed on the video data by the dot correction unit 7 in the internal I / F 6 as described later.

On the operation panel 35, there are provided switches and indicators (not shown) for controlling data, transmitting the information to the engine driver 4 according to instructions from the operator, and displaying the status of the printer on the indicators. Or

The engine driver 4 receives the dot-corrected video data from the controller 3 via the internal I / F 6 and inputs the video data to the writing unit 26 of the printer engine 5 and a sequence device group 27 such as a charging charger and a developing unit, which will be described later. And the video data required for image writing is input via the internal I / F 6 and output to the writing unit 26, and a signal indicating the state of each part of the engine is input from the synchronization sensor and other sensors 28. It processes and outputs necessary information and a status signal of an error situation (for example, a paper end) to the controller 3 via the internal I / F 6.

Since the operation of the printer engine 5 is already well known, a detailed description will be omitted.

FIG. 1 is a block diagram showing a schematic configuration of the dot correction section 7 which is the image data processing device in FIG. The dot correction unit 7 includes an image data input unit 11, an image determination unit 12, an image correction unit 13, and an image data output unit 14. Then, the input image data from the controller 3 is input to the image data input unit 11 and temporarily stored in a FIFO memory or the like.
Send to 2. This input image data includes multi-valued image data in which each pixel has a density gradation.

The image discriminating unit 12 detects each pixel density of the input multi-valued image data, and inputs only image data having a density equal to or higher than the reference value to the image correcting unit 13 as a correction target. Value image data is not subject to correction,
The image data is output as it is and input to the image data output unit 14.

The image correction unit 14 is provided with a step (jaggy) at the boundary between the black dot area and the white dot area of the binary image data.
Is a circuit that performs smoothing correction to smooth
As described above, various techniques are disclosed and will not be described in detail. However, the above-mentioned Japanese Patent Application Laid-Open No.
It is preferable to use the image data processing device disclosed in Japanese Patent No. 207282.

That is, the line segment shape at the boundary between the black dot region and the white dot region of the image data is recognized, and the characteristics of the line segment shape recognized for each required dot are replaced with a plurality of bits of code information. At least a part of the code information is used to determine whether or not the dot needs to be corrected, and the dot determined to need correction is corrected according to the code information.

The image data output unit 14 is connected to the image discriminating unit 12
The multi-valued image data which is not to be corrected and is input from the image correcting unit 13 and the image data in which the necessary dots have been corrected are combined and output. The corrected output data is sent to the engine driver shown in FIG. 2 and the printer engine 5 forms (prints) an image on a sheet.

The image correcting section 13 calculates the inclination direction of the line segment including the target pixel and the position of the target pixel from the line segment shape of the binary image data centered on the target pixel.
Therefore, it is not possible to effectively perform correction processing on multi-valued image data such as gray scale having a tone at the density of one dot, or on an edge portion of font data overlapping with gray scale image data. Therefore, the image discriminating unit 12 detects the density gradation of each pixel of the input image data, compares it with a reference value of a certain density, and replaces it with binary data.

The image shown in FIG. 3 shows an example in which a character font is included as image data in a grayscale image in which the density of one dot has a plurality of gradations. In FIG. 3, halftone gray portions are shaded for easy understanding. Only the edge portion of the character data needs to be subjected to the smoothing correction. Conversely, if the smoothing process is not performed on the gray scale portion, the tone reproducibility will be higher. Therefore, the image discriminating unit 12 performs a process of extracting a portion having a higher density than the reference value in each pixel of the input image data.

Pixel data having a density higher than the reference value is determined to be pixel data ("1"), and pixels having a density lower than the reference value are determined to be absent ("0"). And retain it separately from the original image data. In the example of FIG. 3, the result of replacing the density gradation with the highest density as the reference value and replacing pixels having the density equal to or higher than the reference value with pixel data as binary data is shown in FIG. In this example, “ABC” representing a character from image data
Is extracted as binary image data,
The image data is sent to the image correction unit 13 as image data to be corrected.

For the binary image data to be corrected, the image correcting section 13 performs smoothing correction of the edge portion, and sends the corrected image data to the image data output section 14. The image data of the pixel for which it is determined by the image determination unit 12 that the density of the pixel is not higher than the reference value is directly output as image data not to be corrected, and sent to the image data output unit 14.

In the case of the image shown in FIG. 3, since the density gradation having the highest density is used as the reference value, an image formed by pixels having a lower density is as shown in FIG. 4B. This image data is directly sent to the image data output unit 14 as image data that is not to be corrected. The image data output unit 14 outputs “AB” corrected by the image correction unit 13.
The character data “C” and the image data not to be corrected from the image discrimination unit 12 are combined and output as corrected output data.

In this manner, the character data portion is subjected to edge smoothing correction processing, and a smooth image with little jaggies is output. Image output is possible.

Next, another example of the image discriminating section in the image data processing apparatus is shown in FIG. This image discriminating unit 12 '
Is a gradation density data comparing unit 15 and a density reference value setting unit 16
Consists of The density reference value setting unit 16 can set an arbitrary density reference value.
Compares the gradation density of each pixel of the input image data with the density reference value set by the density reference value setting unit 16, and the pixels having a higher density are used as the correction target data as the image correction unit 13 in FIG. The pixel having a lower density is output to the image data output unit 14 as it is as data not to be corrected.

In the above-described example, the predetermined density reference value in the image discriminating unit 12 is the same density value as the highest tone density of the input image data, and is higher than that density value, that is, the highest tone density. The data of a certain "black" pixel is extracted as correction target data, and correction processing is performed.

On the other hand, the image discriminating unit 12 'can change and set the reference value of the density for extracting the pixel to be corrected (dot), so that, for example, as shown in FIG. Even in the case of multi-tone image data that is not toned (black), it can be extracted as image data to be corrected as shown in FIG. 7A. FIG. 7B shows an image that is not a correction target in this case.

In these embodiments, the image discriminating unit 1
The image data obtained by correcting the data of the image to be corrected determined by 2 or 12 ′ by the image correcting unit 13 and the data of the image not to be corrected are separately input to the image data output unit 14. In this case, if there is no information on which image is to be output, the image is simply synthesized and output.

In the embodiment shown in FIG. 8, the correction information data indicating that the correction processing has been completed is output together with the corrected image data to the image data for the pixels for which the image correction unit 13 'has corrected the image data to be corrected. To the unit 14.
Based on this information, the image data output unit 14 outputs the corrected pixel data for the pixels that have been subjected to the correction processing, and the input image data for the pixels that have not been subjected to the correction processing and the image data that is not to be corrected. The pixel is output as it is.

Next, further functions of the image data output unit 14 will be described. In normal smoothing correction of binary image data, an image having a step (jaggy) at an edge like an image before correction shown in FIG. 9A is corrected like an image after correction shown in FIG. By changing the density gradation of some of the pixels of the previous image or of some of the surrounding pixels, a process of blurring a step (jaggy) occurring at the edge of the image to make it inconspicuous is performed.

However, when the black image portion to be corrected and the image of intermediate density not to be corrected overlap, as in the image before correction shown in FIG. 10A, the image data shown in FIG. In the processing device, when the image data output unit 14 outputs the pixel data corrected by the image correction unit 13 ′, the corrected pixel data shown in FIG. 10B is output. In some cases, the part of the image that is not subject to correction may change to a lower gradation than before correction,
A defect occurs in which the dots of the intermediate density part appear to be partially white.

In order to solve this problem, in a portion where a pixel of the image data after correction and a pixel that has not been corrected or a pixel not to be corrected overlaps, the density gradation of both overlapping pixels is compared. Means for selecting and outputting a pixel having a higher density gradation. As a result, FIG.
The image of the corrected output data from the image data output unit 14 after correction for the image before correction shown in FIG.
As a result, it is possible to solve the problem that the dots appear to be blank.

[0049]

As described above, according to the present invention, even if the input image data is a grayscale image, the image correction unit for performing the edge smoothing correction is provided by two image correction units.
Can handle value image data. Therefore, since the gradation data of the pixel density does not need to be handled in the correction processing, the function of the correction processing unit can be simplified, and high-speed processing can be performed. In addition, since edge smoothing correction is performed only on an image with a high density gradation in which jaggy is conspicuous, it is possible to prevent an adverse effect such as disturbance of the density gradation caused by performing correction on image data with a low gradation density. Can be.

Further, by making it possible to change the reference value of the density for extracting the image data to be subjected to the smoothing correction, it is possible to correct an image having a density in which jaggies are noticeable at the edges of the image. This makes it possible to perform correction processing on images such as characters and line segments having density gradation.

Further, by replacing the input image data with the correction data only in the portion where the input image has been subjected to the correction processing, the image correction result can be easily reflected on the input image data. Then, when the result of the correction process overlaps a pixel that is not to be corrected, a problem that an image such as a white spot occurs in a halftone image portion can be solved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a dot correction unit that is an image data processing device in FIG. 2;

FIG. 2 is a block diagram showing a schematic configuration of a control system of a laser printer which is an image forming apparatus embodying the present invention, together with a host computer.

FIG. 3 is a diagram illustrating an example of an input image based on multi-valued image data.

4 is a diagram showing an image to be corrected and an image not to be corrected, which are determined by the image determining unit 12 shown in FIG. 1 from the image of FIG. 3;

FIG. 5 is a block diagram illustrating another configuration example of the image determining unit illustrated in FIG. 1;

FIG. 6 is a diagram illustrating another example of an input image based on multi-valued image data.

7 is a diagram illustrating an image to be corrected and an image not to be corrected, which are obtained by determining the image of FIG. 6 by the image determining unit 12 ′ illustrated in FIG. 5;

FIG. 8 is a block diagram showing another configuration example of the dot correction unit which is the image data processing unit according to the present invention.

FIG. 9 is a diagram illustrating a pixel configuration before and after correction of a correction target image.

FIG. 10 is a diagram illustrating an example of a pixel configuration before and after correction of an image including a correction target image and a halftone image that is not to be corrected;

FIG. 11 is a diagram showing a preferable example of a pixel configuration after the correction.

[Explanation of symbols]

 1: host computer 2: laser printer 3: controller 4: engine driver 5: printer engine 6: internal interface 7: dot correction unit (image data processing device) 11: image data input unit 12, 12 ': image discrimination unit 13, 13 ': Image correction unit 14: Image data output unit 15: Tone density data comparison unit 16: Density reference value setting unit

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H04N 1/387 G06F 15/68 310J

Claims (4)

[Claims] 1. An image data processing apparatus comprising: an image data processing apparatus having an image correction unit for performing a smoothing correction for smoothing a step at a boundary portion between a black dot region and a white dot region of image data developed in a bitmap shape. An image discriminating unit that detects each pixel density of multi-valued image data, corrects only image data having a density equal to or higher than a reference value by the image correcting unit, and outputs other multi-valued image data as it is, An image data output unit for combining and outputting the multi-valued image data and the image data corrected by the correction unit. 2. The image data processing apparatus according to claim 1, further comprising means for variably setting a reference value of said density in said image discriminating section. 3. The image data processing apparatus according to claim 1, wherein the image correction unit outputs correction information data indicating whether or not the image correction unit has performed correction for each pixel, and the image data output unit outputs the correction information data. The image data after correction is output as it is for pixels that have been corrected in accordance with the information data, and the input image data is output as is for pixels that have not been corrected and pixels that are not to be corrected. Image data processing apparatus. 4. The printing apparatus according to claim 3, wherein the image data output unit overlaps a pixel of the corrected image data with a pixel that has not been corrected or a pixel that is not to be corrected. An image data processing apparatus comprising means for comparing density gradations of both pixels and selecting and outputting a pixel having a higher density gradation.