JP2002354257A - Image processor, image processing method, recording medium, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a restored image less in the deterioration of image quality from image data subjected to a non-reversible compression processing. SOLUTION: When a bit map pattern coincides with either one of feature detecting bit map patterns for mosquito noise removing processing and jaggy reducing processing, a transformation logic circuit 614 changes the data value of an image signal of an attentional pixel N in an image obtained by expanding image data JPEG compressed by a compression/extension part 207 by referring to the image signal of the attentional pixel N and that of pixels around the attentional pixel N to remove mosquito noise generated at the time of expanding the JPEG-compressed image signal and to reduce a jaggy state on an edge of the image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an image processing apparatus, an image processing method, a recording medium, and a program.
It is suitable for use in laser beam printers, digital copiers, etc., which expand irreversibly compressed image data and output restored images.

[0002]

2. Description of the Related Art An image recording apparatus using an electrophotographic system such as a laser beam printer has been widely used due to many advantages such as high printing quality, quietness and high speed. The spread of the image recording apparatus using the electrophotographic method has become one factor that rapidly expands the field of desktop publishing. Furthermore, in recent years, in addition to improving the resolution of a printer engine, which is a printing mechanism of an image recording apparatus, the image recording apparatus detects edges of characters and figures to be printed and performs smoothing processing or the like to improve image quality. As a result, the printing quality of the image recording device has been dramatically improved as compared with the conventional image recording device.

In recent years, electrophotographic color printers, copiers and multifunction printers have been developed, and images for printing color images related to color image data supplied from a host computer or an image scanner or via a network have been developed. Recording devices have been put to practical use.

Here, for example, 600 dpi (dot / dot)
When printing a full-color image with a resolution of inches, the data amount of a color image per one page of A4 paper is as large as about 120 MB. for that reason,
In an image recording apparatus capable of printing a color image, it is necessary to compress the color image data when transferring or storing the color image data in a memory, and decompress and output the image inside the image recording apparatus when printing. This is advantageous in terms of the time required for data transfer of the image recording apparatus and the memory capacity.

As a method of compressing the color image data, for example, an encoding method of the Base Line System (basic method) proposed by JPEG (Joint Photographic Experts Group) as an international standardization method of color still image coding. (Hereinafter, also simply referred to as “JPEG”). This compression method (JPEG) is designed so that the quantization step becomes smaller in the lower frequency band of the DCT space in consideration of the characteristics of human vision and the generation of frequency components due to the discrete cosine transform (hereinafter, also referred to as “DCT”). Was set. As a result, a restored image can be provided for a halftone image even at a high compression ratio without deteriorating the image quality.

On the other hand, in an image recording apparatus such as a color printer as described above, as a method of reproducing a full-color image having gradation, gradation is expressed by a ratio of print dots and non-print dots in a predetermined area. Some methods such as a dither method, an error diffusion method, and a density pattern method, which are so-called pseudo halftone methods, have been used. Further, in a laser beam printer, the resolution in the main scanning direction can be easily changed. For example, in a laser beam printer, there is a pulse width modulation method that expresses shading by changing the drive pulse width of a laser diode for forming a latent image on a photosensitive drum according to the gradation level of image data. Was. The pulse width modulation method was able to achieve both high gradation and high resolution as compared with the pseudo halftone method represented by the dither method.

However, in order to realize all the gradation expressions by the above-mentioned pulse width modulation method, an information amount of about 8 bits per pixel is required, and the image recording capacity for storing the information is increased. The cost of the device increases. For this reason, a small color laser beam printer achieves a balance between image quality and cost by combining a quasi-halftone method that requires an information amount of about 2 to 4 bits per pixel with a pulse width modulation method. There were many. In such a color image recording device, for example,
By repeating the process of transferring a recording image formed on an image carrier on a recording paper by charging, exposing, and developing a plurality of times, a method of forming a multi-color superimposed image on a recording paper to obtain a color image has been put to practical use. ing.

[0008]

However, in the conventional image recording apparatus as described above, when compression / expansion of image data by JPEG is performed, an image such as a photograph is digitized by an image scanner. DC
Although an effect is obtained for an image in which the transform coefficient (DCT coefficient) obtained by T is concentrated in the low band of the DCT space,
For G (Computer Graphics) images, font information such as characters, CAD (Computer Aided Design) line drawings, etc., large-valued conversion coefficients also occur in the high frequency of the DCT space, and the high frequency coefficients are coarse. Decompression (restoration) by quantization
There is a problem that ringing called mosquito noise occurs as shown in FIG. 15 in the restored image, and the image quality of the restored image is deteriorated.

FIG. 15 is a diagram schematically showing an example of mosquito noise. Here, the mosquito noise is noise that is generated in a portion including a high-frequency component of an image or an edge portion when image data subjected to lossy compression processing is expanded (restored). FIG. 15A shows an original image before compression processing, and FIG. 15B shows an image expanded (restored) after compression by JPEG. FIG. 15 (b)
As shown in FIG. 7, in the restored image, a mosquito noise 9 having a low gradation level is added to a portion having strong edge components of a character or a line drawing.
01 occurs, and the image quality of the restored image deteriorates.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has as its object to obtain a restored image with little image quality deterioration from irreversibly compressed image data. And

[0011]

SUMMARY OF THE INVENTION An image processing apparatus according to the present invention refers to an image signal of a predetermined range including a target pixel of an image obtained by expanding image data subjected to lossy compression processing. Means for determining whether or not an image signal of a pixel in a predetermined range including the pixel of interest referred to by the reference means matches a predetermined image signal pattern; and Changing means for changing the image signal of the pixel of interest, wherein the predetermined image signal pattern includes at least a noise detection image signal pattern for detecting noise generated by the expansion processing.

According to another feature of the image processing apparatus of the present invention, the change unit determines that the image signal of a pixel in a predetermined range including the target pixel matches the noise detection image signal pattern by the determination unit. When it is determined, the image signal of the target pixel is changed to an image signal of the lowest density. Another feature of the image processing apparatus of the present invention is that the noise detection image signal pattern is an image signal pattern for detecting mosquito noise.

According to another feature of the image processing apparatus of the present invention, the predetermined image signal pattern further includes an edge detection image signal pattern for detecting that the target pixel is a pixel forming an edge of an image. It is characterized by including. According to another feature of the image processing apparatus of the present invention, the change unit determines that the image signal of a pixel in a predetermined range including the target pixel matches the edge detection image signal pattern by the determination unit. In this case, the image signal of the target pixel is changed to an image signal of a predetermined density.

According to another feature of the image processing apparatus of the present invention, the change means includes an image signal of a pixel in a predetermined range including the target pixel, a noise detection image signal pattern, It is characterized in that it is possible to independently control whether or not to change the image signal of the pixel of interest according to each determination result with the edge detection pattern.

According to another feature of the image processing apparatus of the present invention, the image processing apparatus further includes an input unit for inputting an image attribute signal indicating an image attribute of the pixel of interest, and the changing unit includes:
When the image attribute signal input by the input means indicates a predetermined image attribute, the image signal of the target pixel is not changed. Another feature of the image processing apparatus according to the present invention is that the image data is JP
It is characterized by being image data that has been subjected to lossy compression processing by the EG method.

The image processing method according to the present invention further comprises a reference step of referring to an image signal of a pixel in a predetermined range including a target pixel of an image obtained by expanding image data subjected to lossy compression processing. A determining step of determining whether an image signal of a pixel in a predetermined range including the pixel of interest obtained in the reference step matches a predetermined image signal pattern; And a changing step of changing an image signal of a pixel, wherein the predetermined image signal pattern includes at least a noise detection image signal pattern for detecting noise generated by the expansion processing.

According to another feature of the image processing method of the present invention, in the changing step, the image signal of a pixel in a predetermined range including the target pixel and the noise detection image signal pattern in the determination step are included. When it is determined that they match, the image signal of the target pixel is changed to the image signal of the lowest density. Another feature of the image processing method of the present invention is that the noise detection image signal pattern is an image signal pattern for detecting mosquito noise.

Another feature of the image processing method of the present invention is that the predetermined image signal pattern further includes an edge detection image signal pattern for detecting that the target pixel is a pixel forming an edge of an image. It is characterized by including. Another feature of the image processing method of the present invention is that, in the changing step, the determining step determines that an image signal of a pixel in a predetermined range including the target pixel matches the edge detection image signal pattern. In this case, the image signal of the target pixel is changed to an image signal of a predetermined density.

Another feature of the image processing method of the present invention resides in an input step of inputting an image attribute signal indicating an image attribute of a target pixel of an image obtained by expanding image data subjected to lossy compression processing. A reference step of referring to an image signal of a predetermined range of pixels including the target pixel, and the image signal of a predetermined range of pixels including the target pixel obtained by the reference step matches a predetermined image signal pattern. A determining step of determining whether or not to perform, and a changing step of changing an image signal of the pixel of interest according to the image attribute signal input in the input step and a determination result in the determining step; The predetermined image signal pattern includes at least a noise detection image signal pattern for detecting noise generated by the decompression processing.

A computer-readable recording medium according to the present invention is characterized in that a program for causing a computer to function as each of the above means is recorded. Another feature of the computer-readable recording medium of the present invention is that a program for causing a computer to execute the processing steps of the image processing method is recorded.

The program of the present invention causes a computer to function as each of the above means. Another feature of the program of the present invention is that the program causes a computer to execute the processing steps of the image processing method.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. The image processing apparatus according to the embodiment of the present invention is applied to, for example, a color laser beam printer 101 as shown in FIG.

FIG. 1 shows a color laser beam printer 10.
FIG. 1 is a block diagram illustrating a configuration of a printing system using No. 1. In FIG. 1, a color laser beam printer 101
Are communicably connected to a host computer 102, an image server 103, and the like via a LAN (Local Area Network) 104.

The host computer 102 starts a document processing program such as a word processor stored in a storage device such as a hard disk (not shown), and processes a document in which graphics, images, characters, tables (including spreadsheets, etc.) are mixed. To create a document. The information of the document created by the above document processing is converted into print information written in a predetermined printer language for printing by the color laser beam printer 101 by a printer driver program (not shown). The print information includes a character code, vector information, image information, and the like. Print information converted by a printer driver program (not shown) is supplied to the color laser beam printer 101 via the LAN 104.

A color laser beam printer 101
Is connected to the image scanner 105. The image scanner 105 is a color laser beam printer 1
An image is read from a document in response to an operation of an operation panel (not shown) included in 01, and an image is read in response to an operation from the host computer 102. The image data read by the image scanner 105 is supplied to the color laser beam printer 101 via the host computer 102 or directly from the image scanner 105 as print information (copy mode). Sometimes.

The image data supplied to and stored in the image server 103 is stored in the host computer 1.
The print information is supplied to the color laser beam printer 101 as print information in response to the operation of the operation panel 02 or the color laser beam printer 101. The image data is transmitted and received after being JPEG-compressed on the supply side.

The color laser beam printer 101 comprises a video controller 106 and a printer engine 107. The video controller 106 generates image information composed of dot data (bitmap data) based on print information supplied from the host computer 102, the image server 103, the image scanner 105, and the like.

The printer engine 107 performs recording by a series of electrophotographic processes, modulates a laser beam according to image information sequentially supplied from the video controller 106, and exposes the modulated laser beam to light. Form a latent image by scanning on the drum,
This is transferred onto a recording paper and then fixed. The printer engine 107 has a resolution with a scanning line density of 600 dpi. The color laser beam printer 101
May have a card slot (not shown) so that an optional font card or a control card (emulation card) having a different language system can be connected in addition to the built-in font.

The video controller 106 and the printer engine 107 are communicably connected by an interface signal line 108 (hereinafter, also referred to as "video interface"). Hereinafter, interface signals input and output between the video controller 106 and the printer engine 107 via the interface signal line 108 will be described. In the following description, the symbol “/” added to the signal name indicates that the signal is a low active signal (“true” at low level “L”).

The / PPRDY signal is output from the printer engine 1
07 is a signal notifying that the printer engine 107 is in an operable state when the power is turned on, and is sent from the printer engine 107 to the video controller 106. The / CPRDY signal is a signal for notifying that the video controller 106 is turned on and the video controller 106 is in an operable state, and is sent from the video controller 106 to the printer engine 107.

The / RDY signal is output to the printer engine 107
Is a signal indicating that a print operation can be started or a print operation can be continued when a / PRNT signal, described later, is received.
7 to the video controller 106. For example, if there is no paper in the paper cassette 412 (no paper), which will be described later, and it becomes impossible to perform the printing operation, the signal becomes “false” (high level).

The / PRNT signal is output from the printer engine 10
7 is a signal for instructing the start of the printing operation or the continuation of the printing operation, and is sent from the video controller 106 to the printer engine 107. Printer engine 1
07 starts the printing operation upon receiving the signal.

The / VSYNC signal is a sub-scan (vertical scan)
A direction synchronization signal, which is sent from the printer engine 107 to the video controller 106. The video controller 106 to which the signal is supplied sends image data in the sub-scanning direction in synchronization with the signal, so that the toner image formed on the drum is synchronized with the sheet in the sub-scanning direction and Transcribed above. / LSYNC signal is
This is a synchronization signal in the main scanning (horizontal scanning) direction, and is sent from the printer engine 107 to the video controller 106.

The VDO [7: 0] signal is an 8-bit image signal, and is sent from the video controller 106 to the printer engine 107. The printer engine 107
The pulse width modulation of the laser is performed according to the signal.

The / STS signal is a signal for transmitting a status, and is sent from the printer engine 107 to the video controller 106. The status is 8
This is a serial signal composed of bits. For example, various states of the printer engine 107 such as a wait state in which the temperature of the fixing unit of the printer engine 107 has not reached a printable temperature, a paper jam state, or a paper cassette absence state are described. This is information for notifying the video controller 106 from the engine 107. When transmitting the signal, a / CCLK signal described later is used as a synchronization signal.

The / SBSY signal is output from the printer engine 10
7 is a signal indicating that the status is transmitted to the video controller 106 using the / STS signal,
From the printer engine 107 to the video controller 106
Sent to

The / CMD signal is a signal for transmitting a command, and is sent from the video controller 106 to the printer engine 107. The command is an 8-bit serial signal. For example, the video controller 106 determines whether the paper feeding mode is a mode for feeding paper from a cassette or a mode for feeding paper from a manual feed slot. Is instruction information to instruct. When transmitting the signal, a / CCLK signal described later is used as a synchronization signal.

The / CBSY signal is output to the video controller 1
Reference numeral 06 denotes a signal indicating that a command is transmitted to the printer engine 107 using the / CMD signal, and is transmitted from the video controller 106 to the printer engine 107.

The / CCLK signal is output from the printer engine 10
Reference numeral 7 denotes a synchronization pulse signal for capturing a command or for the video controller 106 to capture a status, and is output from the video controller 106.

Next, the printer engine 107 will be described. FIG. 2 shows the printer engine 1 shown in FIG.
FIG. 7 is a diagram showing a configuration of the third embodiment.

In FIG. 2, a photosensitive drum 401 as an image carrier and a roller charger 402 are arranged in the printer engine 107. On the left side of the photosensitive drum 401, a plurality of developing units 403M, 403C, 403Y, 4
03BK is disposed on a concentric circle centered on the rotation axis 404r of the rotatable support 404.

The developing units 403M, 403C, 403
Y and 403BK contain magenta (M), cyan (C), yellow (Y), and black (K) toners as developing materials, respectively.
03C, 403Y, and 403BK are driven such that the developing opening surface always faces the surface of the photosensitive drum 401.

On the right side of the photosensitive drum 401, a transfer drum 405 having a function of holding a recording paper (not shown) and transferring an image formed on the photosensitive drum 401 onto the recording paper is arranged. With the above configuration, the photosensitive drum 401 is driven to rotate in a direction indicated by an arrow shown in FIG.

The roller charger 402 has about -700
A voltage in which an alternating voltage of 1000 Hz and a peak-to-peak (Vpp) of 1500 V is superimposed on a DC voltage of V is applied, and the surface of the photosensitive drum 401 has a voltage of about -700 V
Is uniformly charged.

Above the printer engine 107, an optical unit 406 and a folding mirror 410, which constitute an exposure device, are arranged to form an optical scanning system. The optical unit 406 includes the laser diode 40
7, a rotating polygon mirror 408 driven by a high-speed motor (not shown) and an imaging lens 409.

The above optical scanning system will be described in detail with reference to FIG. FIG. 3 is a top view of the optical scanning system. Note that the folding mirror 410 is not shown for convenience of explanation. In FIG. 3, a 600 dpi, 8-bit multi-valued image signal VDO7 to VDO0 is output from an image clock VC.
The laser drive signal VD having a pulse width corresponding to the gradation level is input to the pulse width modulation circuit 501 in synchronization with the LK signal.
O is input to the laser driver 502. The density of the image is reproduced according to the pulse width of the laser drive signal VDO.

Next, the laser driver 502 drives the laser diode 407 ON / OFF according to the input laser drive signal VDO, and the laser beam 411 output from the laser diode 407 is shown in FIG. The light is deflected in the direction of the arrow by a rotary polygon mirror 408 driven by a motor (not shown). The rotating polygon mirror 408
The laser beam changed by the above scans the photosensitive drum 401 at a constant speed in the main scanning direction via the imaging lens 409 arranged on the optical path, and forms a latent image on the photosensitive drum 401. At this time, the beam detector 503 detects a scanning start point of the laser beam, and generates a horizontal synchronization signal / LSYNC for determining an image writing timing of main scanning from a detection signal as a detection result.

By repeating the above-described main scanning operation, a magenta (M) latent image for one page is formed on the photosensitive drum 401. Here, the photosensitive drum 401
The portion irradiated with the laser beam is approximately −100 V. When the photosensitive drum 401 rotates in the direction of the arrow shown in FIG. 1, the developing device 403M containing the magenta toner
Thereby, the toner image is visualized.

Next, the transfer step will be described with reference to FIG. First, recording paper (not shown) fed from a paper cassette 412 by a pickup roller (not shown) is held by a gripper 413 and then electrostatically attracted to a transfer drum 405 by a suction roller 414 to which a voltage is applied. The toner image on the photosensitive drum 401 is transferred onto the recording sheet attracted to the transfer drum by a voltage applied to the transfer drum 405 from a power supply (not shown). Further, by performing the above steps for cyan (C), yellow (Y), and black (K), a multicolor toner image is formed on the recording paper.

The recording paper on which the multicolor toner image has been formed is separated from the transfer drum 405 by a separation claw 415 via a separation charger 419, and further fused by a known heating and pressure fixing device 416. The sheet is fixed and discharged from the discharge tray 417. As a result, a color image is recorded on the recording paper.

Thereafter, the transfer residual toner on the photosensitive drum 401 is cleaned by a known cleaning device 420 such as a fur brush or blade means. Also, the transfer drum 4
It is desirable that the toner remaining on the surface 05 be cleaned by a transfer drum cleaning device 417 such as a fur brush or a web.

Subsequently, the photosensitive drum 401 is neutralized and initialized. Here, when the photosensitive drum 401 is to be neutralized, the static elimination is performed by setting the DC voltage to approximately 0 V while keeping the AC voltage applied to the roller charger 402 for charging the photosensitive drum 401. The transfer drum 405 is neutralized and initialized by the neutralization roller 418.

Next, the video controller 1 shown in FIG.
06 will be described in detail. FIG. 4 is a block diagram showing a configuration of the video controller 106 shown in FIG.

In FIG. 4, reference numeral 201 denotes a network interface (hereinafter, referred to as “network I / F”).
And performs communication with other devices communicably connected via the LAN 104 and transmission and reception of print commands and image data. Reference numeral 202 denotes a scanner interface, which performs communication and transmission / reception of image data when the image scanner 105 is operated and controlled by an operation unit 211 described later.

Reference numeral 203 denotes a CPU that controls the entire video controller 106, and reference numeral 204 denotes a ROM that stores a control program for the CPU 203, font data, and the like. Reference numeral 205 denotes a RAM, which serves as a main memory and work area of the CPU 203, a storage area for JPEG-compressed image data, and a band memory for sequentially storing image data (image information) for printing generated by a drawing unit 206 described later. Function. The RAM 205 may be configured so that the memory capacity can be expanded by an optional RAM connected to an additional port (not shown).

Reference numeral 206 denotes a drawing unit which analyzes print information supplied from the host computer 102 via the network I / F and generates multi-valued bitmap image data of 8 bits for each color of RGB for printing. Having. A compression / decompression unit 207 performs the compression / decompression processing of the RGB image data. Reference numeral 208 denotes a hard disk drive (HDD) which stores image data, form data of a fixed form document, font data, and the like supplied from the outside.

An image processing unit 209 includes a color conversion unit 301, a dither processing unit 302, and a smoothing processing unit 303, as shown in FIG. FIG. 5 will be described later.

Reference numeral 210 denotes a printer interface.
An interface circuit for transmitting and receiving predetermined data, control signals, and the like to and from the printer engine 107. Reference numeral 211 denotes an operation unit. By operating the operation unit 211, an operator can directly perform operations such as copying and image reading, and various settings for the printer engine 107. The transmission and reception of data between the blocks in the video controller 106 are performed via the system bus 212.

FIG. 5 is a block diagram showing the configuration of the image processing unit 209. In FIG. 5, a color conversion unit 301 converts RGB image data supplied via a system bus 212 into M (magenta), C (cyan), Y (yellow), K
(Black) (hereinafter also referred to as “MCYK”)
The data is converted into 8-bit data corresponding to each toner. The dither processing unit 302 performs 4-bit multi-value dither processing on the data of each of the MCYK colors. The smoothing processing unit 303 performs smoothing processing by pattern matching on the image data dithered by the dither processing unit 302.

Next, the process of generating image information by the video controller 106 will be described. First, a case will be described in which print information generated by the host computer 102 is developed into bitmap image data inside the color laser printer 101 and printed.

One page of print information supplied from the host computer 102 (consisting of a character print command, a graphic drawing command, image data obtained by reading a photograph, and the like).
Is input to the drawing unit 206 in the video controller 106 via the network I / F 201. Here, the image data is JPEG-compressed RGB image data.

The drawing unit 206 to which the print information has been supplied.
Based on print information such as a character print command, a graphic drawing command, and image data, expansion of outline font data stored in the ROM 204 or the HDD 208, vector expansion of graphics, and expansion of image data by the compression / decompression unit 207 are performed. Is performed to develop the image into 8-bit RGB bitmap image data. In parallel with the decompression process, the compression / decompression unit 207 sequentially compresses the decompressed bitmap image data by JPEG and stores it in the RAM 205. This allows the print data for one page to be converted to JPEG
The compressed RGB image data is stored in the RAM 205.

On the other hand, when printing the image read from the image scanner 105 as it is (copy mode)
Contains the RGB data read by the image scanner 105.
The image data composed of each color is transmitted to the scanner I / F2.
The data is supplied to the compression / decompression unit 207 via J. 02 and is JPEG-compressed by the compression / decompression unit 207 and stored in the RAM 205.

As described above, one page of JPE
When the G-compressed print data is stored in the RAM 205, the video controller 106
07, if the / RDY signal is "true",
The PRNT signal is set to “true” and output to the printer engine 107 to instruct the printer engine 107 to start a printing operation.

At the same time, the video controller 106
Inside the JPEG stored in the RAM 205
The compressed print data is sequentially expanded by the compression / expansion unit 207 again from the data of the first line of the page. The print data expanded by the compression / expansion unit 207 is
The output rate at which the print data is output to the printer engine 107 is written into the RAM 205 again in order to match the output rate with the print speed of the printer engine 107. When print data for a predetermined number of lines (bands) is accumulated, the vertical synchronization signal / VSYN output at a predetermined timing from the printer engine 107 which has received the / PRNT signal.
In synchronization with C, image data is sequentially read from the main scanning first line from the RAM 205 and input to the image processing unit 209.

During this time, the expansion of the print data of the next band by the compression / expansion unit 207 and the processing of writing to the RAM 205 are simultaneously performed. In this way, when the processing of one band is completed, the next band is processed continuously, so that one page is not synchronized with the printing speed of the printer engine 107 without having a memory capacity of one page. Image data can be output (band processing).

The image processing unit 209 supplied with the image data sequentially read from the main scanning first line from the RAM 205 firstly converts the input RGB image data into MCYK color toners by the color conversion unit 301 shown in FIG. Are converted into 8-bit data.

Next, 4-bit multi-value dither processing is performed on the magenta (M) plane by the dither processing unit 302 to generate 4-bit bitmap image information per pixel. Here, the dither processing is a method which is widely used as a pseudo halftone processing method of multi-valued image information. By comparing input multi-valued data with a threshold matrix, whether or not the dot is hit or not is determined. decide.

The threshold matrix (screen) includes:
Although a dot concentration type and a dot dispersion type are known, in an electrophotographic color printing, an oblique line screen having a good balance of gradation and granularity is standard. The threshold matrix (screen) has a resolution for characters with priority given to resolution, and an attribute signal A that can be set for each pixel.
It can be selected by TR.

Here, when the processing of magenta (M) for one page is completed, processing for each of the cyan (C), yellow (Y), and black (K) planes is successively performed. The above threshold matrix (screen)
In order to change the gamma characteristic of each color toner and to change the screen angle for each color, different MCYKs are prepared.

As described above, the 4-bit image signal CVDO multi-value dithered by the dither processing unit 302
[0] to CVDO [3] (hereinafter referred to as CVDO [3: 0] when collectively describing the four bits) are supplied to the smoothing processing unit 303. The above image signal CV
DO [3: 0] has a value of “0” (all bits are “0”).
Indicates white (the minimum density of each color), and "15" (all bits are "1") indicates the maximum density of each color.

Hereinafter, the function and operation of the smoothing processing unit 303 will be described in detail. The smoothing processing unit 303 performs elimination of mosquito noise generated at the time of compression / expansion and smoothing of edges of characters and figures on 600 dpi, 4-bit dithered image information.
7 is converted into an 8-bit image signal to be supplied to the.

FIG. 6 is a block diagram showing a configuration of the smoothing processing unit 303 shown in FIG. In FIG.
Reference numerals 601 to 608 denote first to eighth line memories, respectively. The first to fourth line memories 601 to 604
Is the image signal C supplied from the dither processing unit 302
VDO [3: 0] has a capacity capable of storing one line of main scanning. Further, the fifth to eighth line memories 6
Reference numerals 05 to 608 each have a capacity capable of storing an image signal that has been converted into two bits by a quaternizing circuit 609, which will be described later, for one line of main scanning.

A quaternizing circuit 609 (609a to 609e)
Are based on the 4-bit image signal CVDO [3: 0] supplied from the dither processing unit 302 and the first to fourth line memories 601 to 604, and indicate four types of states when the pixel is subjected to smoothing processing. Has a function of converting the image signal into a 2-bit image signal indicating which of the two states is in.

Reference numeral 610 denotes a memory control circuit for controlling writing, reading, and the like of the first to eighth line memories 601 to 608. Reference numeral 611 denotes a crystal oscillator that supplies a clock signal. Reference numeral 612 denotes a main scanning synchronization signal / LSYN supplied from the printer engine 107 based on the clock signal supplied from the crystal oscillator 611.
This is a synchronous clock generation circuit that generates an image clock signal VCLK synchronized with C.

Reference numeral 613 denotes 9 dots × 9 around the target pixel N.
A shift register group for referring to the image signals of the pixels of the line, and outputs the image signals while shifting them in the main scanning direction according to the image clock signal VCLK supplied from the synchronous clock generation circuit 612. A conversion logic circuit 614 converts the image signal of the target pixel N into an image signal SD [1: 0] obtained by removing noise and smoothing by a predetermined logic with reference to the image signal output from the shift register group 613. And has the function of outputting.

Reference numeral 615 denotes a first bit conversion circuit, which converts the 2-bit smoothed image signal SD [1: 0] supplied from the conversion logic circuit 614 into an 8-bit image signal for supplying to the printer engine 107. Convert. A second bit conversion circuit 617 converts the 4-bit image signal supplied from the delay circuit 616 into the printer engine 10.
7 is converted into an 8-bit image signal to be supplied to the.

Reference numeral 618 denotes a selector for selecting which of the 8-bit image signals supplied from the first and second bit conversion circuits 615 and 617 is to be supplied to the D flip-flop circuit 619. The D flip-flop circuit 619 is for outputting the image signal VDO [7: 0] selected by the selector 618 in synchronization with the image clock signal VCLK. Delay circuit 61
Reference numeral 6 denotes a delay circuit that delays an input signal by five clocks and outputs the delayed signal.

FIG. 7 shows the quaternary circuit 609a shown in FIG.
FIG. 3 is a block diagram showing the configuration of FIG. In FIG.
Reference numerals 702 and 702 denote threshold setting tables, each of which is constituted by a register capable of setting a set value from the outside. In the threshold value setting table 701, a low density side threshold value for considering the pixel as a “white” pixel at the time of edge smoothing processing to be described later is set in advance.
At the time of the edge smoothing process, a high-density-side threshold for considering the pixel as a “black” pixel is set in advance.

The setting range of the set values of the threshold tables 701 and 702 is the lower three of the image signal CVDO [3: 0].
"0" to "7" corresponding to bits. Note that the set value is usually set to a high-density threshold value such that only a portion having a maximum density edge on a white background is processed in order to avoid interference with the threshold matrix (screen) used in the dither processing unit 302 described above. It is preferable to set “7” and the low-density threshold = about “0” to “2”.

Reference numerals 703 and 704 denote 3-bit digital comparators, each of which outputs "1" when the value of the input A is equal to or larger than the value of the input B. The input value of the threshold setting table 701 (low-density threshold) is input to the input A of the digital comparator 703, and the input B is input to the image signal CVDO [2: 0] (lower order of the image signal CVDO [3: 0]). 3 bits) are input. The input A of the digital comparator 704 receives the image signal CVDO [2: 0], and the input B receives the set value (high-density threshold) of the threshold setting table 702.

Reference numeral 705 denotes a NOT circuit, and reference numeral 706 denotes a selector. The selector 706 selects and outputs the input from the digital comparator 704 when the SEL input is “1”, and outputs N when the SEL input is “0”.
An input from the digital comparator 703 via the OT circuit 705 is selected and output.

Next, the operation of the quaternary circuit 609a will be described. The most significant bit CVDO [3] of the input image signal CVDO [3: 0] is directly converted to a quaternary circuit 609a.
, And is used as the selection signal SEL of the selector 706.

On the other hand, the input image signal CVDO [3:
0] are input B of the digital comparator 703 and the digital comparator 704
Of the threshold setting tables 701 and 7
02 is compared with the set value of the digital comparator 70.
3 and 704 respectively. That is, the digital comparator 703 outputs “1” when the value of the image signal CVDO [2: 0] is less than the low density side threshold set in the threshold setting table 701. Further, the digital comparator 704 outputs “1” when the value of the image signal CVDO [2: 0] is equal to or higher than the high-density threshold set in the threshold setting table 702. Thus, the low-density threshold for the image signal CVDO [3: 0] is “0”.
To "7" can be set, and "8" to "15" can be set as the high density side threshold.

The output of the digital comparator 703 is inverted by the NOT circuit 705 and input to the selector 706, and the output of the digital comparator 704 is input to the selector 706 as it is. The above selector 706
Then, the most significant bit CV of the image signal CVDO [3: 0]
Digital comparator 70 inverted by DO [3]
Either the output of 3 or the output of the digital comparator 704 is selected and becomes the lower bit D [0] of the output data (image signal) of the quaternary circuit 609a.

That is, when the value of the input image signal CVDO [3: 0] is "0" to "7", the selector 706 selects the low-density data (the inverted output of the digital comparator 703). , Image signal CVDO [3: 0]
Is between "8" and "15", the high-density data (the output of the digital comparator 704) is selected.

The value of the 2-bit output data D [1: 0] obtained as described above has the following meaning. Output data D = “3”: “black” (high density) pixel during edge smoothing processing Output data D = “2”: halftone pixel (dark) Output data D = “1”: halftone pixel (light) Output Data D = “0”: “white” (low density) pixel during edge smoothing processing

The quaternary circuits 609b to 609b shown in FIG.
609e has the same configuration as the above-described quaternary circuit 609a, and a description thereof will be omitted.

Next, the operation of the smoothing processing section 303 in the above configuration will be described. Dither processing unit 302
Is supplied to the smoothing processing unit 303 in synchronization with the image clock signal VCLK generated by the synchronous clock generation circuit 612 (input).

The image signals CVDO [3: 0] of the first line and the first dot input to the smoothing processing unit 303
Is written into the first line memory 601 and is converted into an image signal D [1: 0] by the quaternizing circuit 609a and input to the first bit (I on the ninth line) of the shift register group 613. Next, the memory control circuit 610
Increments the addresses of the first to eighth line memories 601 to 608 and outputs the image signals CVDO [3: 0] of the first and second dots to the first line memory 6.
Write to 01. At this time, the shift register group 6
The image signal D [1: 0] input to the first bit of No. 13 is shifted (H of the ninth line), and the image signal CVDO of the first line and the second dot is output by the quaternizing circuit 609a.
The image signal D [1: 0] obtained by converting [3: 0] is input to the first bit of the shift register group 613.

The above operation is repeated, and the image signals CVDO [3: 0] of the first line are sequentially stored in the first line memory 601.
And the image signal D [1: 0] obtained by converting the image signal CVDO [3: 0] of the first line by the quaternizing circuit 609a is sequentially input to the image signal D
The data is input to the shift register group 613 shifting [1: 0].

Then, the image signal CVDO of the first line
When the writing of [3: 0] is completed, in the next main scan, prior to the input of the image signal CVDO [3: 0] for the second line, the first line memory 601 stored in the first line memory 601 is used. The image signal at the same position in the line is read. Then, the input image signal of the second line is written into the first line memory 601, and the first line memory 6
01 is read from the second line memory 6
02 is written to the same address. The operation of reading data one line before from a certain address and writing new data to the same address is performed during one cycle of the image signal.

The image signals CVDO [3: 0] of the second and first lines are converted to a quaternary circuit 609.
a, 609b, are converted into image signals D [1: 0] of the second and first lines, and the first bit (I of the ninth line) and the second bit (the eighth line) of the shift register group 613, respectively. Of I).

As described above, the image signal CVDO [3: 0] input for each line is stored in the first line memory 6.
01 → second line memory 602 →... → eighth line memory 608, and writing and reading are performed while shifting. However, after the fifth line memory 605, the image signal to be written and read is an image signal converted into two bits by the quaternary circuit 609e. In this manner, the first to eighth line memories 601 to 608 store image signals for eight consecutive lines. For example, a static RAM can be used as the line memory.

Of the line data synchronized as described above, the input image signal CVDO [3: 0] and the image signals CVDO [3: 0] up to the fourth line are converted to a quaternary circuit 60.
9 (609a to 609e) to generate a 2-bit image signal D
[1: 0] is input to the shift register group 613. Further, the fifth to eighth line memories 605 to 608
Is output to the shift register group 613 as it is.

The shift register group 613 converts a 2-bit image signal for a total of 81 pixels, that is, 9 dots in the main scanning direction and 9 lines in the sub-scanning direction, around the printing pixel (target pixel) N into the VCLK signal. Output while shifting. Here, the column numbers in the main scanning direction of the output data (2-bit image signal) of the shift register group 613 are sequentially set to A, B, C, D, E, F, G, H,
Name it I. The row numbers in the sub-scanning direction are set to 1, 2, 3, 4, 5, 6, 7, and 8 in order from the data of the oldest line, that is, the output of the eighth line memory 608, and the latest quaternary circuit 609a The line number of the line output from is named 9. Each pixel is referred to as “row / column”. That is, the image signal of the print pixel (target pixel) N is the image signal of the fifth row and fifth column, and is “5E”. Therefore, there is a delay of four lines in the main scanning from the time when the image signal CVDO [3: 0] is input to the smoothing processing unit 303 to the time when it is actually printed.

Output data (2-bit image signal) from the shift register group 613 is converted by the conversion logic circuit 6.
14 is input. The conversion logic circuit 614 refers to the image signals of a total of 81 pixels, that is, 9 dots in the main scanning × 9 lines in the sub-scanning output from the group of shift registers 613, and converts the image signal of the target pixel N (“5E” It is determined whether or not the pixel has a value to be changed. If the pixel is to be changed, the smoothed image data SD [1: 0] and the smoothed data designation signal SDATA are output.

Hereinafter, the conversion logic in the conversion logic circuit 614 will be described in detail. The conversion logic circuit 614 changes the data value of the target pixel N according to the state of the surrounding pixels so that the edges of the characters and figures are smoothed as described above. To change the data value of the target pixel N, the output data (binarized image signal) of the shift register group 613 is compared with a plurality of predetermined bitmap patterns for feature detection. Group 613
When the output data (binarized image signal) matches any of the above-described feature detection bitmap patterns, the data value of the pixel of interest N is changed to the smoothed image data SD [1: 0].
It is changed to.

The logic for changing the data value of the pixel of interest N further includes processing for removing mosquito noise generated during the compression / expansion processing, and the printer engine 107.
The processing is divided into two processings of jaggy reduction processing depending on the print resolution of.

First, a feature detection bitmap pattern for mosquito noise removal processing will be described. FIGS. 8A to 8F show an example of a feature detection bitmap pattern for mosquito noise removal processing.

In FIGS. 8A to 8F, “▲” indicates
The binarized image signal D [1: 0] of the pixel is “3”
(= Black) or “2” (halftone / dark), and “Δ” indicates that the image signal D [1: 0] of the pixel is “0” (= white) or “1” ( Halftone / light). In FIGS. 8A to 8F, any other pixel (blank pixel) may be any image signal.

The output data of the shift register group 613 (2
When the valued image signal) matches any of the bitmap patterns shown in the above (a) to (f), the conversion logic circuit 614 outputs the target pixel N (shown by a thick frame in FIG. 8). In order to change the image signal of “0” (= white),
It outputs the smoothed image data SD [1: 0] = "0" and outputs the smoothed data designation signal SDATA. Note that, as the bitmap patterns shown in FIGS. 8A to 8F, patterns that are symmetrical in the upper, lower, left, and right directions are prepared.

According to the logic of the conversion logic circuit 614,
FIG. 9 shows the result of converting the image subjected to the compression / expansion processing. In FIG. 9, (a) is an image before compression processing, and (b)
Is an image when only the decompression processing is performed, and (c) is an image when the decompression processing and the mosquito noise removal processing are performed. As shown in FIG. 9, the mosquito noise removal processing shown in FIG.
Since 1 is replaced by white data, the image shown in (c) obtained as a result is an image close to that before the compression processing shown in (a). Note that whether to enable the mosquito noise removal processing can be controlled by a control signal NCON shown in FIG.

Next, a feature detection bitmap pattern for jaggy reduction processing will be described. The feature detection bitmap pattern for the jaggy reduction process detects whether or not the target pixel N and its surrounding pixels form an edge of the image and are near a hatched change point. An example of a bitmap pattern for feature detection for jaggy reduction processing is shown in FIGS.

In FIGS. 10 and 11, “•” indicates that the binarized image signal D [1: 0] of the pixel is “3”.
(= Black), and “○” indicates that the image signal D [1: 0] of the pixel is “0” (= white). The other pixels (blank pixels) may be any image signal. The feature detection bitmap pattern is configured by, for example, a well-known AND-OR circuit.

For example, in the case of the bit map pattern shown in FIG. 10A, the conversion logic circuit 614 determines that the target pixel N is a part of the hatched edge near the horizontal (in the main scanning direction) Assuming that it is a change point on the density side, smoothed image data SD [1: 0] = "3" is output, and a smoothed data designation signal SDATA is output.
Similarly, in the case of the bitmap patterns shown in FIGS. 10B and 10C, the conversion logic circuit 614 determines that the smoothed image data SD [1: 0] = "2" and the smoothed image data SD [1: 0] = “1”, and outputs the smoothed data designation signal SDATA.

For example, in the case of the bitmap pattern shown in FIG. 11A, the conversion logic circuit 614 determines that the target pixel N is a part of the left edge of the oblique line near the vertical (sub-scanning direction) and Assuming that there is a change point on the high density side, the smoothed image data SD [1: 0] = "2" is output, and the smoothed data designation signal SDATA is output.
Similarly, in the case of the bitmap patterns shown in FIGS. 11B and 11C, the conversion logic circuit 614 sets the smoothed image data SD [1: 0] = “2” and the smoothed image data SD [1: 0] = “1”, and outputs the smoothed data designation signal SDATA. Note that whether to enable the jaggy reduction processing can be controlled by a control signal SON shown in FIG.

The bitmap patterns shown in FIGS. 10 and 11 are examples of the bitmap pattern for feature detection for the jaggy reduction processing, and many other bitmap patterns are prepared. As for the bitmap patterns shown in FIG. 10 and FIG. 11, similarly to the above-described bitmap pattern for removing mosquito noise, symmetric patterns in the vertical and horizontal directions are prepared.

The smoothed image data SD [1: 0] output from the conversion logic circuit 614 is converted by the first bit conversion circuit 615 into an 8-bit image signal to be supplied to the printer engine 107. The first bit conversion circuit 615 converts, for example, the smoothed image data SD [1: 0] as follows. SD [1: 0] = “3” → C0H SD [1: 0] = “2” → 80H SD [1: 0] = “1” → 40H SD [1: 0] = “0” → 00H It is preferable that the converted value of the smoothed image data SD [1: 0] by the first bit conversion circuit 615 is configured to be register-settable from outside.

The 8-bit image signal converted by the first bit conversion circuit 615 is supplied to the selector 618, and is selected by the selector 618 by the smoothing data designation signal SDATA. Then, the 8-bit image signal supplied from the selector 618 to the D flip-flop 619 is synchronized with the image clock signal VCLK by the D flip-flop 619 and the image signal VDO [7:
0].

On the other hand, for pixels that do not match any of the above-described feature detection bitmap patterns for mosquito noise removal processing and jaggy reduction processing, the image signal VDO output from the smoothing processing unit 303 is used.
As [7: 0], the image signal of the target pixel N (= 5E) is applied.

More specifically, the image signal CVDO [3: 0] output from the fourth line memory 604 is delayed by five clocks by the delay circuit 616, and the shift register group 6
Signal 5E_OR whose timing has been matched with the output from 13
G [3: 0] is supplied to the second bit conversion circuit 617. Further, the second bit conversion circuit 615 converts the signal 5E_ORG [3: 0] into an 8-bit image signal to be supplied to the printer engine 107, and the selector 618.
To supply. Note that the converted value of the signal 5E_ORG [3: 0] by the second bit conversion circuit 617 is preferably configured to be register-settable from outside.

The 8-bit image signal supplied from the second bit conversion circuit 617 to the selector 618 is converted by the selector 618 into the smoothed data designation signal SDATA.
Is "0", the D flip-flop 619 is selected.
, And in a D flip-flop 619, synchronized with the image clock signal VCLK, the image signal VDO [7:
0].

Here, when the control signal NCON is “0”, the conversion logic circuit 614 outputs the shift register group 613
, The smoothed data designation signal SDATA always outputs "0", even if the output data of the data and the bitmap pattern for mosquito noise removal processing match. Similarly,
When the control signal SON is “0”, the conversion logic circuit 61
4 indicates that the smoothed data designation signal SDATA is always "0" even if the output data of the shift register group 613 matches the bitmap pattern for jaggy reduction processing.
Is output. Thereby, the control signals NSON and SO
When N is “0”, the logic conversion circuit 614 does not change the data value by the processes corresponding to the control signals NSON and SON, respectively.

The 8-bit image signal VDO [7: 0] output from the D flip-flop 619 is supplied to the printer engine 107, and the value of the image signal VDO [7: 0] is output from the printer engine 107 as described above. The above-described electrophotographic recording in which an image for each color is generated by the pulse width modulation processing according to the above and transferred to a sheet is performed.

An example of a smoothed image obtained by the jaggy reduction processing as described above is shown in FIGS.
FIG. Figure 1 shows the case where the image is a horizontal diagonal line
FIG. 13 shows the case of oblique lines close to vertical as shown in FIG. FIGS. 12 and 13 show a case where the input is a single-plane binary image for convenience of explanation.

12A and 13A, FIG.
This is a restored image based on the original image signal of 00 dpi (no smoothing process), and (b) is a restored image that has been smoothed by the conversion logic circuit 614. FIG.
In FIG. 13 and FIG. 13, one cell of the grid indicates a unit of one dot of 600 dpi.

As shown in FIGS. 12 and 13, smoothing processing is performed so that an edge of an image is formed in a restored image, and a change point in a hatched portion is changed stepwise.
In addition, fine pulse-shaped intermediate density dots hit at the edge change points are blurred without being resolved at the time of development due to the relationship between the energy distribution of the photosensitive drum and the particle size of the developer (toner). The resulting image is printed smoothly as shown by the dotted line in FIG.

As described above in detail, according to the present embodiment, the conversion logic circuit 6 in the smoothing processing unit 303
Reference numeral 14 denotes a mosquito noise removal process and a jaggy reduction process by referring to the target pixel N of the image obtained by expanding the image data JPEG-compressed by the compression / expansion unit 207 and the image signals of the surrounding pixels. If it matches any of the feature detection bitmap patterns for
The data value of the image signal of the target pixel is changed, and the selector 61
8, an image signal obtained by converting the image signal of the target pixel whose data value has been changed is output.
Mosquito noise generated when the EG-compressed image signal is expanded can be removed, and jaggies at the edges of the image can be reduced. Therefore,
A restored image with little image quality degradation can be obtained from the JPEG-compressed image signal, and a high-quality print output can be obtained. Further, since a basic circuit for the mosquito noise removal processing and the jaggy reduction processing can be shared, it can be realized at a low cost with a simple configuration.

In the present embodiment, the case of a color laser beam printer has been described. However, the present invention is not limited to a color laser beam printer, but may be a laser beam type copier, an LED printer, a liquid crystal shutter type printer, or a color printer. The present invention can also be applied to an image processing apparatus in another type of recording apparatus such as an inkjet type printer.

Also, in the present embodiment, the JPEG compression method is used for image data. However, the present invention is not limited to this.
It can be applied to irreversibly compressed image data. Further, in the present embodiment, when determining whether to change the data value of the target pixel N with reference to the image signal of the target pixel N and its surrounding pixels, a total of 9 dots in main scanning × 9 lines in sub-scanning are determined. Although the image signal for the pixel is referred to, the present invention is not limited to this, and it is possible to determine whether to change the data value of the target pixel N with reference to the image signal for an arbitrary pixel. it can.

Further, in the above-described embodiment, the smoothing processing unit 304 performs processing for a document or the like in which graphics, images, characters, tables (including spreadsheets, etc.) are mixed, in an image area and a character area. Regardless, all areas are smoothed. However, as shown in FIG. 14, an image attribute signal ATR for discriminating between an image area and a character area is provided, and smoothing processing may be performed only on a character area. good.

FIG. 14 is a block diagram showing the configuration of the smoothing processing unit 303 'for performing the smoothing processing only on the character area as described above. In FIG. 14,
Blocks having the same functions as the blocks shown in FIG. 6 are denoted by the same reference numerals, and redundant description will be omitted. Also,
Blocks that are not the same as the blocks illustrated in FIG. 6 but have corresponding functions are denoted by the same reference numerals.

In FIG. 14, the smoothing processing unit 30
The image attribute signal ATR is input to 3 ′ in addition to the 4-bit image signal CVDO [3: 0]. Here, when the image attribute signal ATR is "1", the image signal CV
DO [3: 0] is an image signal of a character area,
"0" indicates that the image signal CVDO [3: 0] is an image signal of an image area.

The input image attribute signal ATR is supplied to the first to fourth line memories 601 'to 604' and the delay circuit 616 'together with the image signal CVDO [3: 0]. In addition, the same processing as that of the smoothing processing unit 303 shown in FIG. 6 is performed on the image signal CVDO [3: 0].

The image attribute signal ATR delayed by the delay circuit 616 'and the smoothed data designating signal S
An AND operation with DATA is performed by an AND circuit 1401, and a result of the AND operation is used by a selector 618 to output the smoothed image data SD output from the conversion logic circuit 614.
One of the converted 8-bit image signals is selected based on [1: 0] and the image signal of the target pixel. Thus, when the image attribute signal ATR is “0” (image area), an 8-bit image signal obtained by converting the smoothed image data SD [1: 0] output from the conversion logic circuit 614 can be selected. The smoothing processing by the smoothing processing unit 303 'is not performed on the image area. Therefore, when the smoothing processing unit 303 'shown in FIG. 14 is used, interference with the screen in the image image can be avoided by prohibiting the smoothing processing in the image area.

(Other Embodiments of the Present Invention) In order to operate various devices in order to realize the functions of the above-described embodiments, an apparatus connected to the various devices or a computer in a system is connected to the above-described embodiment. Supply the software program code to realize the functions of
The present invention also includes those implemented by operating the various devices according to a program stored in a computer (CPU or MPU) of the system or apparatus.

In this case, the software program code itself implements the functions of the above-described embodiment, and the program code itself and means for supplying the program code to the computer are provided.
For example, a recording medium storing such a program code constitutes the present invention. As a recording medium for storing such a program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-RO
M, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the supplied program code, not only the functions of the above-described embodiment are realized, but also the OS (operating system) or other operating system running on the computer. Needless to say, even when the functions of the above-described embodiments are realized in cooperation with application software and the like, such program codes are included in the embodiments of the present invention.

Further, after the supplied program code is stored in the memory provided in the function expansion board of the computer or the function expansion unit connected to the computer, the function expansion board or the function expansion unit is stored based on the instruction of the program code. It is needless to say that the present invention also includes a case where the CPU or the like provided in the first embodiment performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0131]

As described above, according to the present invention,
An image signal of a predetermined range of pixels including a target pixel of an image obtained by decompressing image data subjected to lossy compression processing is a predetermined image including a noise detection image signal pattern for detecting noise generated by the decompression processing. It is determined whether or not it matches the signal pattern, and the image signal of the target pixel is changed according to the determination result. This makes it possible to remove noise generated at the time of decompression processing of image data that has been subjected to lossy compression processing, and to obtain a high-quality restored image with little image quality deterioration.

Further, when the predetermined image signal pattern includes an edge detection image signal pattern for detecting that the pixel of interest is a pixel forming an edge of the image, the jaggy of the edge of the image is reduced. As a result, a high-quality restored image with little image quality degradation can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a printing system using a color laser beam printer 101.

FIG. 2 is a diagram illustrating a configuration of a printer engine 107.

FIG. 3 is a top view of an optical scanning system in the printer engine 107.

FIG. 4 is a block diagram showing a configuration of a video controller 106.

FIG. 5 is a block diagram illustrating a configuration of an image processing unit 209.

FIG. 6 is a block diagram illustrating a configuration of a smoothing processing unit 303.

FIG. 7 is a block diagram illustrating a configuration of a quaternary circuit 609a.

FIG. 8 is a diagram illustrating an example of a feature detection bitmap pattern for mosquito noise removal processing.

FIG. 9 is a diagram showing a restored image after mosquito noise removal processing.

FIG. 10 is a diagram illustrating an example of a feature detection bitmap pattern for jaggy reduction processing.

FIG. 11 is a diagram showing another example of a bitmap pattern for feature detection for jaggy reduction processing.

FIG. 12 is a diagram illustrating an example of a smoothed image after jaggy reduction processing.

FIG. 13 is a diagram illustrating another example of an image in which a jaggy reduction processing word is smoothed.

14 is a block diagram illustrating another configuration example of the smoothing processing unit 303. FIG.

FIG. 15 is a diagram schematically illustrating an example of mosquito noise.

[Explanation of symbols]

 Reference Signs List 101 color laser beam printer 102 host computer 103 image server 104 LAN 105 image scanner 106 video controller 107 printer engine 108 interface signal line 601 to 608 line memory 609 quaternary circuit 610 memory control circuit 611 crystal oscillator 612 synchronous clock generation circuit 613 shift Register group 614 Conversion logic circuit 615 First bit conversion circuit 616 Delay circuit 617 Second bit conversion circuit 618 Selector 619 Flip-flop

Continued on the front page F term (reference) 5B021 AA01 AA19 CC06 CC08 LG08 5B057 AA20 BA02 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC01 CE02 CG05 DB02 DB06 DB09 DC08 DC16 5C077 LL02 PP55 PQ12 PQ20 RR21 SS03 TT02 TT02

Claims (18)

[Claims] A reference unit for referring to an image signal of a pixel in a predetermined range including a target pixel of an image obtained by decompressing image data which has been subjected to lossy compression processing; Determining means for determining whether or not an image signal of a pixel in a predetermined range includes a predetermined image signal pattern; and changing means for changing an image signal of the pixel of interest according to a determination result by the determining means An image processing apparatus, wherein the predetermined image signal pattern includes at least a noise detection image signal pattern for detecting noise generated by the decompression processing. 2. The image processing apparatus according to claim 1, wherein the determining unit determines that the image signal of the pixel of interest in the predetermined range including the pixel of interest coincides with the noise detection image signal pattern. 2. The image processing apparatus according to claim 1, wherein the image signal is changed to an image signal having the lowest density. 3. The image processing apparatus according to claim 2, wherein the noise detection image signal pattern is an image signal pattern for detecting mosquito noise. 4. The image processing apparatus according to claim 1, wherein the predetermined image signal pattern further includes an edge detection image signal pattern for detecting that the target pixel is a pixel forming an edge of an image. The image processing apparatus according to claim 1. 5. The changing means, when the determining means determines that the image signal of a pixel in a predetermined range including the pixel of interest coincides with the edge detection image signal pattern, changes the image signal of the pixel of interest. The image processing apparatus according to claim 4, wherein the image signal is changed to an image signal having a predetermined density. 6. The changing means according to each of the determination results of the image signal of a pixel in a predetermined range including the pixel of interest and the noise detection image signal pattern and the edge detection pattern by the determination means. The image processing apparatus according to claim 4, wherein whether or not the image signal of the target pixel is changed can be independently controlled. 7. An image processing apparatus further comprising: input means for inputting an image attribute signal indicating an image attribute of the pixel of interest, wherein the changing means determines whether the image attribute signal input by the input means indicates a predetermined image attribute. 2. The image signal of the pixel of interest is not changed.
The image processing apparatus according to any one of claims 1 to 6. 8. The image processing apparatus according to claim 1, wherein the image data is image data subjected to irreversible compression processing by a JPEG method. 9. A reference step of referring to an image signal of a pixel in a predetermined range including a target pixel of an image obtained by expanding image data subjected to lossy compression processing, and a target pixel obtained by the reference step A determination step of determining whether an image signal of a pixel in a predetermined range including a predetermined image signal pattern matches a predetermined image signal pattern, and changing the image signal of the pixel of interest according to the determination result in the determination step An image processing method, comprising the steps of: 10. The image signal of the pixel of interest when it is determined in the determination step that the image signal of a pixel in a predetermined range including the pixel of interest matches the noise detection image signal pattern. 10. The image processing method according to claim 9, wherein is changed to an image signal having the lowest density. 11. The noise detection image signal pattern includes:
The image processing method according to claim 10, wherein the image signal pattern is an image signal pattern for detecting mosquito noise. 12. The image signal pattern according to claim 9, wherein the predetermined image signal pattern further includes an edge detection image signal pattern for detecting that the pixel of interest is a pixel forming an edge of an image. 2. The image processing method according to claim 1. 13. The image signal of the pixel of interest when it is determined in the determination step that the image signal of a pixel in a predetermined range including the pixel of interest matches the edge detection image signal pattern. 13. The image processing method according to claim 12, wherein is changed to an image signal having a predetermined density. 14. An inputting step of inputting an image attribute signal indicating an image attribute of a pixel of interest of an image obtained by expanding image data subjected to lossy compression processing; A reference step of referring to an image signal; a determination step of determining whether an image signal of a pixel in a predetermined range including the target pixel obtained in the reference step matches a predetermined image signal pattern; and the input step And a changing step of changing the image signal of the pixel of interest in accordance with the image attribute signal input in step (a) and the determination result in the determining step, wherein the predetermined image signal pattern is generated by the decompression process. An image processing method comprising at least a noise detection image signal pattern for detecting noise. 15. A computer-readable recording medium on which a program for causing a computer to function as each of the means according to claim 1 is recorded. 16. A computer-readable recording medium on which a program for causing a computer to execute the processing procedure of the image processing method according to claim 9 is recorded. 17. A program for causing a computer to function as each means according to claim 1. Description: 18. A program for causing a computer to execute the processing procedure of the image processing method according to claim 9. Description: