JP2000184205A - Image forming system and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming system that applies proper compression to each kind of an image element so as to make image quality compatible with a compression rate. SOLUTION: Job data in the page description language(PDL) expressing an original picture 100 are copied and the job data are independently interprete- processed to generate a character graphic plane 150a of an image consisting of visible parts of character-graphic elements of the original picture, an image plane 150b consisting of an image of image elements such as a natural picture, and binary map data 150c where a level '1' is set to pixels of the visible parts of the character-graphic elements and a level '0' is set to the other pixels. The data 150a-150c are generated by allowing the same PDL interpreter to interpret the job after re-defining the interpretation of an image drawing operator for the character-graphic elements and the image elements. Applying a proper compression method to the character graphic plane 150a and the image plane 150b respectively rather than applying the same compression method to the entire original picture 100 can obtain high image quality and a high compression rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a system for forming an image on a medium from a job described in a page description language, and more particularly to a technique for reducing the amount of transmission data such as a network in the system.

[0002]

2. Description of the Related Art In recent years, in the field of high-speed and high-performance printer systems for business use and the like, a front-end processor (hereinafter abbreviated as FEP) and a back-end processor (hereinafter B).
There are many system configurations that use a combination of two types of processing devices called "EP". The FEP receives a print job described in a page description language (PDL) from a client device, interprets the job, and generates intermediate format image data. On the other hand, the BEP is a module that is connected to a print engine that performs a printing operation on paper and controls the print engine. The BEP converts the intermediate format image data generated by the FEP into final format image data that can be handled by the print engine, and supplies the final format image data to the print engine. The FEP and the BEP are both connected to a network such as a LAN, and image data is transmitted from the FEP to the BEP via the network.

[0003] Such an FEP-BEP configuration can be regarded as a configuration in which a PDL interpretation portion and a printer engine control portion of a conventional general print engine are configured as separate modules. It is suitable for a system configuration using a high-speed and high-performance print engine from the viewpoint of efficient use of the image data.

That is, it is more efficient to operate the print engine continuously, and this point is remarkable in the case of an electrophotographic print engine, for example. On the other hand, the job from the client comes intermittently.
Therefore, if job interpretation and print engine control are performed by the same device as a print server, the print engine must be suspended while no job arrives or while load is imposed on job interpretation. , Inefficiency. On the other hand, in the configuration divided into FEP and BEP, the print engine can be operated independently of the job interpretation processing in the FEP, so that the print engine can be operated efficiently.

Further, this configuration has an advantage that flexibility of the system configuration can be obtained. For example, when a new print engine is introduced into an existing system, it has conventionally been necessary to introduce an expensive print server having a job interpretation function.
It is only necessary to introduce EP. By appropriately adjusting the number of FEPs and the number of BEPs and print engines according to the properties of print jobs (color / black and white, resolution) and print engine performance that are frequently handled, it is possible to construct a system suitable for specifications required by customers. .

[0006]

In recent years, the amount of data that travels between FEP and BEP has been dramatically increased with higher image quality and higher resolution of printing.
The communication load on the network due to data transmission between BEPs cannot be ignored. For this reason, FEP,
It is indispensable to compress and transmit image data between BEPs.

[0007] There are roughly two types of compression schemes. One is a lossless compression method such as the LZW (Lempel-Ziv-Welch) method. Generally, the reversible compression method has an advantage that an image having a small density change and a large number of repetitive components, such as characters and graphics (graphics), can be compressed at a high compression rate, and the original image can be restored without deterioration. However, natural images (for example, when a photo is scanned by a scanner)
Such an image having a small number of repetitive components is not suitable because a high compression ratio cannot be realized. Another compression method is a lossy compression method such as JPEG. Generally, the irreversible compression method has an advantage that a continuous tone image such as a natural image whose density changes relatively randomly can be compressed at a high compression ratio. When an image is compressed by this method, high-frequency components are removed, so the restored image is slightly deteriorated as compared to the original image, but such deterioration is not a problem in image quality in a natural image or the like. . However, in the case of characters and figures, a decrease in high-frequency components causes dulling of edges, which may cause a problem in image quality.

[0008] In the printing field, characters,
It is common for graphics and continuous tone images such as natural images to coexist, but in such cases, compression with sufficient compression ratio and quality can be achieved using either the lossless compression method or the irreversible compression method. No results can be obtained. As a method for compressing a page in which text / graphics and natural images are mixed at a high compression rate while maintaining quality, the type of image elements (also called objects) (that is, text / graphics or natural images) It has been proposed to use different compression methods depending on the situation.
At present, there is no specific system configuration for realizing this for the following reasons.

That is, when the image of one page is separated and compressed for each image element (or for each type) on the FEP side, it is necessary to synthesize these image elements on the BEP side. The vertical relationship (overlap) between the elements must be determined on the FEP side and reported to the BEP side. However, in order to realize this using a single PDL interpreting mechanism, it is necessary to make a large change to the PDL interpreting mechanism itself on the FEP side, which is not realistic in terms of cost and the like.

The present invention has been made in view of such circumstances, and has as its object to provide a system that performs appropriate compression for each type of image element and achieves both image quality and a compression ratio.

In order to solve the above-mentioned problems, according to the present invention, an interpreting module (for example, the above-described FEP) for interpreting a job described in a page description language and generating an image receives the job from a client device. A means is provided for duplicating the required (or stored) PDL jobs by the required number. Then, the same print job obtained as a result is interpreted and rendered in parallel by changing the types of image elements to be interpreted and rendered. "Parallel" here
Means that each interpretation / drawing process is performed completely independently without synchronization or message exchange. Therefore, not only parallel processing in terms of time but also cases where processing is performed at different times are included in the concept of the present invention when such processing is performed independently.

The processing to be performed in parallel includes a processing of drawing a first image composed of visible portions of a first type of image element group and a processing of rendering a second image composed of a second type of image element group. And a process of generating map data for identifying a pixel in which a visible portion of the first type of image element group exists. For example, the first type of image element is a character / graphic element, and the second type of image element is a sampling image element (hereinafter, referred to as an image element). Alternatively, the reverse is also possible. The character / graphic element is an image element with a small density change represented by a character or a graphic and having many repetitive components, and the image element is an image represented by a natural image and having a small repetitive component. The type of the image element can be distinguished by the type of the drawing operator in the PDL. The “visible portion” of the first type of image element group is a portion of those image elements that is not covered by the second type of image element.

The system of the present invention includes means (first drawing means, second drawing means, map generation means) for performing each of these processes. These means are constructed based on existing page description language processing means also called an interpreter or a decomposer. These units generate the first image, the second image, and the map data by sequentially interpreting the copied job in the same manner as the normal interpretation / drawing process. Therefore, the first image, the second image, and the map data include information on the vertical relationship (overlap) of each image element,
It becomes what is held explicitly or implicitly.

The first image is subjected to compression processing suitable for the first type of image element by the first compression means. As a result, a first compressed image is obtained. The second image is subjected to a compression process suitable for the second type of image element by the second compression unit. As a result, a second compressed image is obtained. For example, a reversible compression method such as LZW using data repetition is suitable for character / graphic elements. For image elements, an irreversible compression method such as JPEG utilizing correlation in an image of a natural image is suitable in terms of a compression ratio. Since the map data only needs to include information for identifying a pixel where the first type of image element exists or is not a pixel, the data amount is small. Therefore, there is little need for data compression for map data. However, compression of this is also within the scope of the present invention.

In the interpretation module, the three data of the first compressed image, the second compressed image, and the map data are obtained from one job. These are sent to a reproduction module (for example, the aforementioned BEP) in association with each other.

In the reproducing module, the first compressed image and the second compressed image are decompressed by using the decompression method corresponding to the compression method used for each compression, and the first image and the second image are reproduced. Then, referring to the map data, the value of the corresponding pixel of the first image is selected for a pixel where the visible portion of the first type of image element exists, and the other pixels are selected for the corresponding pixel of the second image. By selecting the value, the first and second images are combined. The obtained composite image is an image originally represented by the PDL description of the job.

For example, the case where the first type of image element is a character / graphic element and the second type of image element is an image element will be described. Means that the character / graphic element is the first
Since it appears in the image and can be identified as a pixel of a character / graphic element even in the map data, the character / graphic element is drawn also at the corresponding pixel of the composite image. Conversely, when the image element is overwritten on a part of the character / graphic element, the part of the character / graphic element where the image element is overwritten is not a visible part, and is not drawn on the first image. Similarly, the map data is not identified as a pixel of a character / graphic element. Therefore, for the pixel of the overwritten portion, the corresponding pixel value of the second image is selected in the composite image (that is, the effect of overwriting the image element appears). By supplying the composite image to the print engine and printing it, an image equivalent to an image obtained by directly interpreting a job can be obtained.

According to this configuration, since an appropriate compression method can be applied to each type of image element (object), a high compression ratio and image quality can be achieved at the same time. In addition, the first image, the second image, and the map data naturally reflect the vertical relationship of each image element by duplicating the job and independently interpreting / drawing each image. There is no need for a mechanism for separately extracting information on the upper / lower relationship of each image element and transmitting the information to the playback module. Therefore, only a small change is required for the existing page description language processing means. Moreover, this change is not an essential change of the algorithm, but may be a minor change that changes the definition of the interpretation of some drawing operators in the means, as described later. Such a change (redefinition) of the definition is originally planned by a general page description language processing means, and can be dynamically performed.

In a preferred aspect, the first and second drawing means,
The map generating means is obtained by redefining (changing) the interpretation of some drawing operators in a predetermined page description language processing means.

In order to obtain the first drawing means for drawing the first image, for example, the drawing operator of the second type of image element can be set by changing the image element to the background color (that is, that no image is drawn on the paper). The color to be expressed, for example, the pixel value “0”) may be redefined so as to be interpreted as drawing or filling processing. The rendering operator's interpretation of the first type of image element does not change. The page description language processing means (that is, the first drawing means) which has performed such redefinition is provided with the PD of the job.
By causing the L description to be interpreted from the beginning and performing a drawing process, a first image consisting of the visible portion of the first type of image form element is obtained. In this example, if a second type of image element is later overlaid on a first type of image element, and as a result the first type of image element becomes invisible, the first type of image will be included in the first image. The element does not appear (that is, the area of the background color indicating the second type of image element is overwritten and nothing is drawn). As described above, in this configuration, a complete job is processed without any change except for changing the interpretation of some operators. Therefore, the first image element and the second image element are included in the first image. Is stored. The vertical relationship between the first type of image elements is of course preserved.

Further, in order to obtain the second drawing means for drawing the second image, a drawing operator for the first type of image element is required.
The predetermined page description language processing means may be redefined so as to be interpreted as drawing omission (that is, processing in which drawing is omitted and processing other than drawing has the same effect as the original operator). As a result, only the second type of image element is drawn at an accurate position. In this example, since a complete job is processed without any change except for a change in the interpretation of some operators, it is possible to draw each image element of the second type while maintaining the vertical relationship with each other. .

Further, in order to obtain the map generation means, the rendering operator of the first type of image element is interpreted as processing for rendering the element in a binary image format, and the rendering operator of the second type of image element is interpreted. May be redefined to interpret the element as a process of drawing or filling the element with a background color. This means, except that the first type of image element is drawn as a binary image,
The processing is the same as that of the drawing means. Therefore, map data for selecting only the visible portion of the first type of image element is obtained by the same mechanism as the first drawing unit.

In one embodiment of the present invention, the same page description language processing means is redefined by the rendering operator according to the purpose of the first rendering means, the second rendering means, and the map generation means each time, and the repetitive operation is performed. By doing so, the functions of the first drawing unit, the second drawing unit, and the map generation unit can be obtained. According to this aspect, the functions of three means can be obtained by one page description language processing means,
The cost of the interpretation module can be reduced.

If the first drawing means, the second drawing means, and the map generation means are constructed using different page description language processing means, and a system configuration for completely parallel processing is adopted, the processing speed can be improved. Can be expected. The fact that such parallel processing is possible is a feature of the present invention that the first drawing unit, the second drawing unit, and the map generation unit can proceed with the processing completely independently of each other.

[0024]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.
In the following, as an example of a page description language, PostScript (registered trademark of Adobe Systems, Inc., USA) will be described. However, the present embodiment does not depend on a specific page description language. It goes without saying that it is basically applicable to any page description language. Note that the description of PostScript is limited to the minimum necessary for the description of the present embodiment. Therefore, when it is necessary to know the details of the language specifications and the like, for example, “PostScript Reference Manual Second Edition” (by Adobe Systems, See Adobe Systems Japan, ASCII, Inc.).

<Page Description Language> The page description language has various drawing operators (also called paint operators).
However, in general, they can be roughly divided into a sampling image element drawing operator and a character / graphic element drawing operator.

Here, a sampling image element (hereinafter, abbreviated as an image element) is an image element represented by a rectangular array of sampling values. Here, each sampling value represents a color (pixel value). The image element is obtained from a scanner device, a digital camera, or the like, and is generally a continuous tone image such as a natural image (such as a photograph). Post
In Script, for example, an image operator is a representative of a drawing operator of this image element.

On the other hand, a character / graphic element is an image element such as a character or graphic (graphics) represented as a locus or a painted area. In PostScript, for example, show (for character drawing), fill (for area filling), st
roke (for drawing line diagrams), imagemask (for drawing binary masks)
An operator or the like is a representative of the character / graphic element drawing operator.

<Processing Principle of Embodiment> In this embodiment,
The front-end processor (FEP) compresses the character / graphic element and the image element in the page by applying an appropriate image compression method, and compresses the compressed data into a back-end processor (BEP). We propose a system to transfer to. The processing principle of the system will be described with reference to FIG.

An original image 100 represented by a PDL description of a job includes various image elements (drawing objects) such as a character element 110, a graphic element 120, and an image element 130.
Shall be included.

In this embodiment, the FEP generates three types of data from the job: a character / graphic plane 150a, an image plane 150b, and map data 150c. The character / graphic plane 150a is an image composed of a visible part of the character / graphic element (that is, a part not covered by the image element).
Is an image composed of image elements. Map data 1
Reference numeral 50c denotes a binary bitmap image in which a pixel corresponding to a visible part of a character / graphic element has a value of 1 (black) and other pixels have a value of 0 (white, that is, background color). The resolutions of these three images are equal, and pixels between each other are 1 pixel.
It corresponds to one to one. Each of these images can be generated by processing the same job data by changing the interpretation of some drawing operators (details will be described later). For this reason, in the present embodiment, a mechanism for duplicating a required number of job data received from the client is provided.

Since these three types of images are obtained by sequentially processing the same job data, information on the upper limit relationship between image elements is stored. In FEP, characters
A compression method such as LZW is applied to the image of the graphic plane 150a.
The image of the image plane 150b is subjected to image compression using a compression method suitable for the image in the plane, such as a compression method such as JPEG. Then, the obtained compressed data of each plane is transmitted to the BEP together with the map data.

In the BEP, the compressed data of each plane is decompressed by an appropriate decompression method, and the resulting images 150a and 150b of each plane are mapped to map data 150c.
To generate a composite image 200. The synthesis processing is performed by selecting the pixel value of the character / graphic plane 150a for the pixel having the value 1 in the map data, and selecting the pixel value of the image plane 150b for the pixel having the value 0 in the map data. Then, the print engine prints the composite image.

According to such processing, an appropriate compression method can be used according to the type of image element, and both a compression ratio and image quality can be achieved. In addition, since the information of the upper / lower (overlapping) relationship between the same job image elements is naturally reflected in the planes 150a and 150b and the map data 150c, a complicated mechanism for managing the upper / lower relationship is required. do not do. The image represented by the job can be reproduced simply by performing the above-described synthesis processing.

<Overview of System Configuration> FIG. 2 is a diagram showing a schematic configuration of the image forming system according to the present embodiment.
In FIG. 2, a LAN (local area network)
The network 50 includes a front-end processor (FEP) 10, a back-end processor (BEP) 2
0, the client device 30 is connected. In the figure,
Although only one FEP 10, one BEP 20, and one client device 30 are shown, any number of them can be connected to the network 50. FEP10, BEP
How many are connected to each other is determined based on specifications required by customers.

FEP 10 is a page description language (PDL)
Is an apparatus that interprets the print job described in (1) and generates image data of each page, and can be constructed using software based on a computer. The FEP 10 receives a print job issued by a printer driver or the like of the client device 30, and generates a page image of each page based on the print job. Then, image compression is performed on the page image, and the resulting compressed image data is
Send to

The BEP 20 is connected to a print engine 40 for performing a hard copy process on a sheet.
The compressed image data transmitted from 10 is decompressed, adjusted to a format that can be handled by the print engine 40, and supplied to the print engine 40. The BEP 20 can also typically be built on a computer. Below, FEP
The detailed configuration of the BEP 10 and the BEP 20 will be described.

<Details of FEP> (1) Duplication of Job The FEP 10 includes a job management unit 12, a job duplication unit 14,
First drawing unit 16a, second drawing unit 16b, third drawing unit 16
c, including a first compression unit 18a and a second compression unit 18b. The job management unit 12 receives PDL jobs sent from the client device 30 and performs spooling and other management on these jobs. The job is transferred to the job duplication unit 14 via the job management unit 12. The job duplicator 14 duplicates the received job and generates three identical job data. Each of these job data is
First drawing unit 16a, second drawing unit 16b, third drawing unit 16
c. These drawing units 16a to 16c
Processes the received jobs in parallel.

(2) Character / graphic plane The first rendering unit 16a interprets the received job in order from the top, and renders (marks) the visible portion of the character / graphic element on the page on a memory (not shown). ), And generates an image of a character / figure plane. This processing is performed by drawing a character / graphic element as it is, and filling an image element with a background color in a frame that defines the range of the element.

The first drawing unit 16a is a PDL processing unit called a PDL interpreter or a decomposer.
This can be realized by changing (that is, redefining) the definition of the interpretation of some drawing operators. Specifically, characters
The drawing operator for graphic elements (show, stroke, etc.) is not changed, and the drawing operator for image elements (imag
e) is redefined to be interpreted as a process of filling a frame defining the range of the element with a background color. By default, the image element drawing operator represents a process of painting a bitmap image prepared in advance in the area. In the present embodiment, since only the area of the image element needs to be known, the area is painted with the background color. It is redefined as processing. In this area, a bitmap image of a corresponding image element is drawn at the time of synthesis in the BEP 20.

In the PostScript processing means (interpreter), for example, a stack is used as a job control structure. When a redefined operator is processed, the original stack is stored in the stack. This is performed so that the same effect as when the operator is processed remains. The same applies to the redefinition of the second drawing unit 16b and the third drawing unit 16c to be described later.

When the job is interpreted in order from the top by the first drawing unit 16a constructed by such redefinition, finally, the character / graphic element group is not covered by the image element. Only the part that can be seen (that is, the visible part) is drawn on the memory. This drawing result is called a character / graphic plane image. Even when the character / graphic elements overlap each other, the uppermost part finally appears on the character / graphic plane as a visible part. The first drawing unit 16a does not change the algorithm itself of the PDL processing means, but simply changes the interpretation of the drawing operator, so that the processing result of the job is the same as the drawing result by the PDL processing means without change. The vertical relationship between the image elements is maintained. The character obtained
The graphic plane image is passed to the first compression unit 18a.

The first compression section 18a performs compression processing on the received character / graphic plane image by a reversible compression method such as the LZW method. Plain text / graphic images are
Since the image is composed of the visible part of the graphic element, the image has many repetitive components and the edge of the image is sharp. Therefore, the reversible compression method using repetition of information is an appropriate compression method from the viewpoint of both compression efficiency and image quality (edge information storage). The reversible compression method that can be used in the first compression unit 18a is not limited to the LZW method.

The compressed image data of the character / graphic plane obtained by the compression processing in the first compression section 18a is sent to the BEP 20 via the job management section 12.

(3) Image Plane The second drawing unit 16b interprets the received job in order from the top, draws image elements in a page on a memory, and generates an image of an image plane. This processing is performed by drawing only the image element without drawing the character / graphic element.

Similarly to the first drawing unit 16a, the second drawing unit 16b can be realized by redefining the interpretation of a part of the drawing operator of the PDL processing means. This redefinition may be performed so that the character / graphic element drawing operator becomes invalid. That is, it is redefined as a process that does not perform drawing in the memory. Here, the operator to be redefined is P
If the specification is such that the internal state of the DL processing means is changed, the internal state based on the processing result of the operator after the redefinition is the same as the internal state based on the processing result of the original operator. An operator who changes the internal state includes, for example, an operator who moves a current point or clears a path in PostScript. Note that attention to the internal state in this redefinition is also considered when constructing the above-described first drawing unit 16a and the below-described third drawing unit 16c.

The second drawing unit 16 thus constructed
When the job is interpreted sequentially in b, an image plane image in which the image element groups are arranged according to the hierarchical relationship implicitly shown in the job is generated. Note that all parts of the image element group are drawn on the image plane image regardless of whether or not the character / graphic element is overwritten. For overwriting text / graphic elements,
It is adjusted at the time of the synthesis processing in the BEP 20. The image plane image obtained in this manner is stored in the second compression unit 18.
b.

The second compression section 18b performs a compression process on the received image plane image by a lossy compression method such as JPEG. Since the image plane image is composed of only image elements, J using the correlation in the image is used.
By the irreversible compression method such as PEG, compression can be performed at a high compression ratio without significantly deteriorating the image quality. The irreversible compression method that can be used in the second compression unit 18b is not limited to JPEG.

The compressed image data of the image obtained by the compression processing in the second compression section 18b is sent to the BEP 20 via the job management section 12.

The first drawing unit 16a described above,
In the second drawing unit 16b, the resolution of drawing and the depth (number of bits) per pixel are determined based on the performance of the print engine 40 to be output.

(4) Map Data The third drawing unit 16c interprets the received jobs in order from the top to generate map data. This map data is a monochrome binary bitmap in which the pixels corresponding to the visible portion of the character / graphic element are “1” (black) and the other pixels are “0” (white, ie, background color). The third drawing unit 16c also has a PD similar to the first drawing unit 16a.
This can be realized by redefining the interpretation of a part of the drawing operator of the L processing means. The processing performed by the third drawing unit 16c is the same as that of the first drawing unit 16c except that the depth (number of bits) per pixel of the generated bitmap image is set to 1 bit.
This is the same process as a. The third drawing unit 16c is a PDL
In the processing means, the drawing operator of the character / graphic element is redefined so as to perform the same processing as the original after changing the color value to black, and the drawing operator of the image element sets the frame defining the range of the element. Is redefined to be interpreted as a process of filling the inside with the background color.

When the job is interpreted in order from the top by the third drawing unit 16c constructed in this way, the pixel corresponding to the visible portion of the character / graphic element is black (1), and the other pixels are the background color (0). ) Is obtained. In this map data, since the number of bits of one pixel is 1, characters and
The data amount is much smaller than the image data of the graphic plane or the image plane. For this reason, there is little need to provide a compression module at a high cost for compressing the map data. Therefore, in the present embodiment, a configuration is adopted in which map data is sent to the BEP 20 without being compressed. Of course, it is also possible to adopt a configuration for compressing the map data, in which case it is preferable to use a lossless compression method such as LZW. The map data generated by the third drawing unit 16c is transmitted to the BEP 20 via the job management unit 12.
Sent to

The resolution of the drawing process in the third drawing unit 16c is the same as the resolution of the drawing in the first and second drawing units 16a and 16b.

(5) Correlation of Data The job management unit 12 associates the compressed data of the character / graphic plane, the compressed data of the image plane, and the map data generated from the same job with each other in BEP2.
Send to 0. There are several methods for this association. For example, when these three pieces of data are completed, they may be transmitted to the BEP 20 collectively. Further, each time such data is received, the identification information of the job and the identification information of the data type (character / graphic, image or map) may be added and transmitted to the BEP 20. In the latter case, it is not necessary to dissolve the job management unit 12, and it is possible to add such identification information in each of the drawing units 16a to 16c and each of the compression units 18a and 18b.

(6) Others The configuration of the FEP 10 described above has the following advantages. That is, in the present embodiment, each of the drawing units 16a to 16
Since c can operate completely independently without mutual synchronization or information exchange, complete parallel processing can be performed, and an improvement in processing speed can be expected.

However, parallel processing is not essential, and one PDL processing means is redefined each time, and the first drawing unit 16
a, the second drawing unit 16b and the third drawing unit 16c may be configured to operate three times. In this case, the duplication of the job does not have to be performed literally, and each time the PDL processing unit operates as each drawing unit, the same job is
What is necessary is just to make it the structure passed to processing means. In this configuration, the processing time may be longer than that of the parallel processing configuration, but the cost of hardware and software resources can be reduced.

Further, by providing queues before and after each of the drawing units 16a to 16c, continuous jobs can be efficiently processed.

<Details of BEP> BEP20 is FEP1
The original image represented by the job is reproduced based on the compressed image data and the map data of the character / graphic plane and the image plane received from 0, and supplied to the print engine 40.

Data from FEP 10 is received by job management unit 22. The job management unit 22 stores
The compressed data of the graphic plane is input to the first expansion unit 24a, the compressed data of the image plane is input to the second expansion unit 24b, and the map data is input to the image synthesis unit 26.

The first decompression unit 24a decompresses the received compressed data of the character / graphic plane using a reversible decompression method corresponding to the compression method of the first compression unit 16a. As a result, the character / graphic plane image is reproduced without deterioration.

The second decompression unit 24b decompresses the received compressed data of the image plane using an irreversible decompression method corresponding to the compression method of the second compression unit 16b. As a result, an image plane image is reproduced.

The image synthesizing unit 26 synthesizes the character / graphic plane image and the image plane image with reference to the map data. In this combination, the map data acts as a selector for determining which value of the corresponding pixel of the character / graphic plane image or the image plane image is selected as the value of each pixel of the composite image. That is, when determining the value of each pixel of the synthesized pixel, the image synthesizing unit 26 examines the corresponding pixel of the map data and determines that the value is 1
In the case of (black), the value of the corresponding pixel of the character / graphic plane image is adopted, and when the value is 0 (white, that is, the background color), the value of the corresponding pixel of the image plane image is adopted.

FIG. 3 is a diagram for explaining the principle of the synthesizing process. In the figure, two lines 2 corresponding to each other are used as an image plane, a character / graphic plane, and map data.
4 shows data of four pixels in a column array. Hereinafter, each pixel is specified by the coordinate system of (row, column). According to the map data, it can be seen that three pixels (0, 0), (0, 1), and (1, 1) are visible portions of the character / graphic element. The image synthesizing unit 26 refers to the map data, selects the pixel values of the character / graphic plane for the three pixels, and selects the pixel values of the image plane for the remaining pixels (1, 0). Create In FIG. 3, in the character / graphic plane, the pixel values of (1, 0) and (1, 1) are 0.
However, these two meanings are completely different. That is, from the map data, (1, 1) corresponds to the visible portion of the character / graphic element, and the value of the character / graphic plane is selected, whereas (0, 1) specifies the other pixels. And the value of the image plane is selected. The former represents a character / graphic element drawn with a background color, and the latter is understood to indicate the absence of the character / graphic element itself. In the example of FIG.
The pixel (1, 1) has a value of 30 in the image plane, but in the composite image, the value 0 of the character / graphic plane is selected by the map data, which is the background overwritten on the image element. Represents the color character / graphic element part.

By such a synthesizing process, an image represented by the original job can be reproduced. That is, FEP1
0, each of the drawing units 16a to 16c processes the same job in order from the beginning and performs drawing. Therefore, when viewed only in the character / graphic plane or only in the image plane, the drawn image The overlapping relationship between the elements satisfies the relationship defined in the original job. The problem is the overlapping relationship between the character / graphic element and the image element, which satisfies the relationship represented by the original job by the method of generating the character / graphic plane, the image plane, and the map data in this embodiment. Will do.

That is, in the present embodiment, when generating a character / figure plane image, the area of the image element is painted with the background color. Therefore, when the character / graphic element is covered by the image element, the covered part does not appear in the character / graphic plane image (that is, the pixel value is 0). Map data differs from character / figure planes only in the number of bits per pixel.
The portion covered by the image element has a pixel value of 0. Therefore, with respect to this part, the data of the image plane is selected at the time of synthesis, and the state where the image element is overwritten is correctly reproduced. Conversely, for the part where the character / graphic element is overwritten by the image element, the text is drawn on the character / graphic plane image, and the value of that part becomes 1 in the map data. Even if there is an image in the portion, the value of the character / graphic plane is adopted. Therefore, the state where the character / graphic element is overwritten on the image element is correctly reproduced. Thus, according to the present embodiment,
In the BEP 20, it is possible to obtain a composite image in which the overlapping (upper / lower) relationship between the image elements in the job is correctly reproduced. The obtained composite image is input to the print engine 40 and printed on a medium such as paper.

In order to operate the image synthesizing unit 26, the output data of the first decompressing unit 24a and the output data of the second decompressing unit 24b must be aligned with the map data. For this reason, for example, the job management unit 22 monitors whether the character / image plane, image plane, and map data for the same job are complete.
It is also preferable to adopt a configuration in which the 4a and 24b and the image synthesizing unit 26 are operated. In addition, a character / graphic plane image, an image plane image,
It is also preferable to provide a queue for map data, and to operate the image synthesizing unit 26 when the three types of data corresponding to the same job are arranged in the queue. With this configuration, there is no need to wait for the decompression processing until all three types of data are collected, so that an improvement in processing efficiency can be expected.

The FEP 10 and BEP 20 shown above are:
Typically, it is constructed by software on the basis of a computer, but each compression unit 18a, 18b and each decompression unit 24
a, 24b, the image synthesizing unit 26, and the like can be relatively easily implemented as hardware.

<Others> The preferred embodiments of the present invention have been described above. In the above example, the lossless compression method is used for an image of a character / graphic element, and the irreversible compression method is used for an image of an image element. However, this is merely an example. The gist of the present invention is to provide a method of performing compression using appropriate different compression methods while preserving the relationship between image elements in view of the fact that an appropriate image compression method differs for each type of image element. Therefore, the character / graphic element is not limited to the lossless compression method, and the image element is not limited to the irreversible compression method (although, in view of the current compression technology, such use is preferred). For example, if there is a case where there is an irreversible compression method suitable for a character / graphic element and the irreversible compression method appropriate for an image element is different from that method, if the two compression methods are used using the method of the present embodiment. Can be used properly.

In the above example, the map data is configured to represent the visible portion of the character / graphic element.
A configuration that reverses this, that is, uses map data representing the visible portion of the image element is also possible. In order to realize this, the generation processing of each plane in the FEP may be changed according to the map format. That is, the first drawing unit 16a that generates the character / graphic plane is the PD
The L processing means is configured by redefining the rendering operator of the image element to be interpreted as invalid (drawing omitted). Further, the second drawing unit 16b that generates the image plane is configured by redefining the PDL processing means so as to interpret the drawing operator of the character / graphic element as drawing / area filling in the background color. The third drawing unit 16c that generates the map data interprets the PDL processing means as the image element drawing operator as black and white binary black and the character / graphic element drawing operator as black and white binary black and white.
It is constructed by redefining the value to be interpreted as filling with white (background color). Other parts may be the same as in the above-described example. With this configuration, the original image represented by the job can be reproduced from the character / graphic plane, the image plane, and the map data according to the same principle as in the above-described example. However, in this modified example, when there is a portion where a character or a graphic element is overwritten on an image element, a corresponding portion on the image plane becomes a white state, and if this is lossy-compressed, the edge of the overwritten portion becomes dull. there is a possibility. Therefore, in terms of image quality, it can be said that the method of the above-described example is a more desirable mode.

In the above description, the system having the FEP-BEP configuration has been described as an example. However, the present invention is also effective when used in a general print server. That is, some print servers have a function of storing and reusing image data generated once from a job. Even with such an apparatus, it is not possible to compress image data at a high compression rate while suppressing deterioration of image quality. is important. Therefore, the application of the present invention to such an apparatus is very significant. As a specific device configuration in this case, for example, a configuration in which the FEP 10 and the BEP 20 in FIG. 2 are integrated by sharing the job management units 12 and 22 is considered.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of an embodiment.

FIG. 2 is a diagram illustrating a schematic configuration of an image forming system according to the embodiment.

FIG. 3 is a diagram for explaining how to use map data.

[Explanation of symbols]

10 front end processor (FEP), 12 job management unit, 16a first drawing unit, 16b second drawing unit,
16c third drawing unit, 18a first compression unit, 18b second compression unit, 20 backend processor (BEP),
22 job management unit, 24a first decompression unit, 24b second decompression unit, 26 image synthesis unit, 30 client device,
40 print engines, 50 networks, 100
Original image, 110 character element, 120 graphic element, 130 image element, 150a character / graphic plane, 150b image plane, 150c map data, 200 composite image.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H04N 1/413 B41J 3/12 C F term (Reference) 2C061 AP01 HH03 HJ06 HK03 HN02 HN15 2C062 AA10 AA14 AA32 AA69 2C087 AA11 BA03 BC02 BC05 BD01 BD09 BD40 5C078 AA01 AA04 CA03 DA01 DA02 9A001 BB02 BB04 CC02 DD02 DZ10 EE02 FF06 HH25 HH27 HH28 JJ35 KK42

Claims (9)

[Claims] An image processing apparatus interprets a job described in a page description language to generate an image, and an interpretation module for compressing the image; reproduces the image from compressed data generated by the interpretation module; A reproduction module for causing a print engine to perform printing, wherein the interpretation module interprets the job and renders a first image including a visible portion of a first type of image element group; A first compression process for generating a first compressed image by performing a first compression process suitable for a first type of image element group on the first image
Compression means; second rendering means for interpreting the job and rendering a second image composed of a second type of image element group; and suitable for the second type of image element group for the second image. A second compression process is performed to generate a second compressed image.
Compressing means; interpreting the job, map generating means for generating map data for identifying pixels in which the visible portion of the first type of image element group exists, duplicating the job received from the client, First
And a job duplicating means for supplying to the drawing means, the second drawing means and the map generating means, wherein the first compressed image generated from the same job,
Outputting the compressed image and the map data in association with each other, wherein the reproduction module performs decompression processing corresponding to the compression processing of the first compression unit on the first compressed image to reproduce the first image. 1
Decompressing means, performing a decompression process corresponding to the compression process of the second compression unit on the second compressed image to reproduce the second image.
Decompressing means, referring to the map data, selecting a value of a corresponding pixel of the first image for a pixel having a visible portion of a first image element group, and selecting a value of a corresponding pixel of the second image for other pixels. Synthesizing means for synthesizing the image represented by the job by selecting the value of the corresponding pixel, and the first compressed image, the second compressed image and the map data corresponding to each other generated by the interpretation module. An image forming system for distributing and processing the first decompressing means, the second decompressing means, and the synthesizing means, respectively, and causing the print engine to perform printing based on an image obtained from the synthesizing means. 2. The method according to claim 1, wherein the first drawing unit, the second drawing unit, and the map generation unit are configured by redefining the interpretation of some drawing operators in a predetermined page description language processing unit. The image forming system according to claim 1. 3. The first drawing means redefines a predetermined page description language processing means such that a drawing operator of the second type of image element is interpreted as a drawing process of the image element with a background color. The image forming system according to claim 1, wherein: 4. The second drawing means redefines a predetermined page description language processing means so as to interpret a drawing operator of the first kind of image element as a processing in which drawing is omitted. The image forming system according to claim 1, wherein: 5. The map generating means interprets a rendering operator of the first type of image element as a process of rendering the image element in a binary image format, and renders the second type of image element. 2. The image forming system according to claim 1, wherein a predetermined page description language processing unit is redefined so that the operator interprets the image element as a process of drawing the image element with a background color. 6. The first drawing means, the second drawing means, and the map generation means, wherein the same page description language processing means is used for interpreting a drawing operator. 2. The image forming system according to claim 1, wherein the image forming system is obtained by redefining the image each time according to the purpose and repeatedly performing the operation. 7. The image processing device according to claim 1, wherein the first type of image element is a character / graphic element, and the second type of image element is a sampling image element. 3. The image forming system according to 1. 8. The image processing apparatus according to claim 1, wherein the first type of image element is a sampling image element, and the second type of image element is a character / graphic element. 3. The image forming system according to 1. 9. An interpreting module that interprets a job described in a page description language to generate an image, compresses the image, and reproduces the image from compressed data generated by the interpreting module. In a system including a reproduction module for causing a print engine to perform printing, a first type is obtained by duplicating a job to generate three job data and interpreting these job data in parallel by an interpretation module. Map data for identifying a pixel in which a visible portion of the first type of image element group, a second image of the second type of image element group, and a second image of the second type of image element group Respectively, and performs a first compression process suitable for a first type of image element group on the first image to generate a first compressed image, and generates the second image. Performing second compression processing suitable for the second type of image element group generating a second compressed image to the first compressed image, the second compressed image and map data,
Immediately after generation or after accumulation, it is passed to the playback module, and the playback module performs the corresponding decompression processing on the first compressed image and the second compressed image, and plays back the first image and the second image. Referring to the map data, the value of the corresponding pixel of the reproduced first image is selected for the pixel where the visible portion of the first image element group exists, and the corresponding pixels of the reproduced second image are selected for the other pixels. A method for controlling an image forming system, comprising: synthesizing an image represented by the job by selecting a pixel value; and supplying an image obtained as a result of the synthesis to a print engine.