JP2001157062A - Image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the transfer speed of a shared bus from becoming the bottleneck in processing. SOLUTION: This image processor for storing inputted image information in a page memory 12 to transfer it to an input part 13 via the shared bus 14 is provided with a compressing part 15 for compressing the image information to generate compressed data and an expansion part 18 for expanding the compressed data to generated expanded data and transfers the compressed data to the part 18 via the bus 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image processing apparatus mounted on an image forming apparatus such as a printer or a digital copier, and more particularly, to an image processing apparatus having a compression function for transfer within a shared bus. .

[0002]

2. Description of the Related Art Conventionally, image data to be printed, which is supplied from a host computer such as a personal computer or a workstation, or an image input device such as an image scanner, performs predetermined image processing before forming an image. Is input to 2. Description of the Related Art In an image processing apparatus such as a printer or a digital copier, each functional unit is mutually connected by a dedicated communication path, and is integrally configured as a system. For example, a scanner that reads a document, a printer that prints on recording paper, and a system control unit that controls the entire system are mutually connected by a dedicated communication path, and are integrally configured. The system control unit and other functional units exchange necessary control information and the like, respectively.
Image data is transferred from the scanner to the printer. That is, since the respective functional units are connected by the dedicated communication path, it is possible to transfer control information and image data between the respective units independently and at necessary timing.

[0003] In contrast to such a system, an architecture in which each functional unit is connected to each other via a shared bus as the copier system becomes more complex and sophisticated, is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-83711. Copier ". FIG. 8 is a block diagram showing a system configuration of a conventional digital copying machine using a shared bus. This system includes a printer 1 that actually performs a printing process, a scanner 2 that reads an original, an SCU 3 that controls the entire system, and a SCSI-2 (Small Computer System Interface) that is a communication path having a bus configuration connecting these components.
rface-2) A bus 4 and a serial communication path 5 for connecting the SCU 3 and the printer 1 for communication.

In the above system, the serial communication path 5
Is performed only during a period in which image data transfer is being performed by the SCSI-2 bus 4. That is, the serial communication path 5 is used to transfer only control information that requires transfer even during transfer of image data. Therefore, since it is only necessary to have the minimum transmission capacity necessary for transmitting control information, a low-cost RS-232C or the like is sufficient.

There are various advantages in such an architecture for connecting each functional unit through a shared bus. In particular, it is excellent in that development costs are reduced and the development period is shortened when upgrading functional units. In other words, if each functional unit is connected only to the shared bus, the interface part of the functional unit can be used as it is when upgrading the version. There is no need to do it.

FIG. 9 is a block diagram showing a schematic configuration of a conventional system based on a shared bus type architecture. This system is mainly composed of a host computer 20 such as a personal computer (PC) or a workstation, and a printer 1 for printing out image data sent from the host computer 20.

The printer 1 stores a page creation buffer 11 provided to convert data received from the host computer 20 into image data suitable for output (writing), and stores at least one page of bitmap data. The configuration is such that a page memory 12 to be used and an output unit 13 that outputs bitmap data stored in the page memory 12 are connected on a shared bus 14.

[0008] Here, as the shared bus, the above-mentioned SCS is used.
In addition to the I-2 bus, for example, PCI (Pe
ripheral Component Interconnect) bus. The PCI bus is a bus that realizes a maximum transfer speed of 133 MB / sec with a 32-bit data bus and a bus clock of 32 MHz. A general-purpose bus is desirable as a shared bus because it is widely used and is inexpensive and has high stability.

[0009]

However, an image processing apparatus in which each functional unit is connected by a shared bus has the above-mentioned excellent features, but on the other hand, the processing speed of the shared bus is limited. Has the drawback of becoming a bottleneck. For example, a PCI bus is used as a shared bus, and one card per second is 1200 dpi.
When a color image of a size (1 bit depth) is to be output, the information amount of the image is 139.2 MB while the transfer speed of the PCI bus is 133 MB / sec.
It is impossible to output image data one sheet per second.

Further, the bus cannot always achieve the highest transfer rate, and the transfer rate is reduced by various factors. Therefore, if the device is manufactured (designed) assuming the maximum performance of the shared bus, the transfer speed cannot keep up with the writing speed of the printer when the transfer speed is reduced for some reason, and as a result, an abnormal image occurs. . To avoid such inconveniences, the transfer speed is usually given a margin, and the device is manufactured (designed) assuming a transfer speed of, for example, about 50% of the maximum performance. However, in this case, the transfer speed (throughput) further decreases, and it is impossible to print as many as 0.5 sheets per second.

For this reason, conventionally, when the transfer speed (throughput) required of the image processing apparatus exceeds the transfer speed of the shared bus, the shared bus is replaced, the bus width is increased, or the clock frequency is increased. By doing
There is a need to improve the performance of the shared bus. However, when the shared bus is replaced, a new interface for connecting the shared bus and the functional unit must be developed, resulting in an increase in manufacturing cost. Also, when you increase the bus width, the design becomes complicated,
In addition, since the number of pins increases, it is necessary to change the interface part. Further, when the clock frequency is increased, there is a problem that stable signal transmission is hindered.

The present invention has been made in view of the above, and a first object of the present invention is to prevent a transfer speed of a shared bus from becoming a bottleneck in processing.

It is a second object of the present invention to be able to cope with a change in the transfer rate required for the image processing apparatus without changing the basic configuration centering on the shared bus.

[0014]

According to another aspect of the present invention, there is provided an image processing apparatus for transferring input image information to an image output unit via a shared bus. An image compression means for compressing the image information and generating compressed data;
Image decompression means for generating decompressed data, wherein the compressed data is transferred to the image decompression means via the shared bus.

According to the present invention, image information to be subjected to image processing (output) is converted into compressed data according to a compression method predetermined by the image compression means, and the compressed data is
By supplying it to the image decompression means and decoding it there,
The data transferred on the shared bus is always compressed data, so that a data amount exceeding the transfer limit of the shared bus can be transferred at high speed.

The image processing apparatus according to claim 2, further comprising a compressed data storage unit for storing the compressed data and outputting the compressed data to the shared bus, wherein the image decompression unit stores the compressed data. The compressed data from the means is expanded.

According to the present invention, image information to be subjected to image processing (output) is converted into compressed data according to a compression method predetermined by the image compression means, and the compressed data is
For example, by storing data in the compressed data storage unit on a page basis and supplying the compressed data storage unit to the image decompression unit via the shared bus, it is possible to handle transfer speeds exceeding the transfer limit of the shared bus when printing the same page multiple times. It is possible to do.

The image processing apparatus according to claim 3, further comprising a plurality of areas divided for each predetermined storage capacity, and storage means for storing decompressed data in the areas. Instructing the page memory to transfer the next predetermined unit of compressed data based on a signal indicating that a predetermined amount of decompressed data has been output from the storage means, and alternately storing a plurality of areas of the storage means, respectively. Transfer control means for switching to an area / readout area.

According to the present invention, for example, when each area of the storage means can store only 10 lines of expanded data, particularly when a compression method in which one code represents a large number of pixel information is used, Since the number of pixels exceeds 10 lines and the memory is over, based on a signal indicating that a predetermined amount of decompressed data has been output from the storage unit,
The next predetermined unit of compressed data (number of pixels) on the page memory side
, The number of pixels at the time of decompression is determined, and each area is alternately switched as a storage area / readout area.

In the image processing apparatus according to a fourth aspect of the present invention, when the decompressed data stored in the storage means exceeds a predetermined number of pixels, the transfer control means reduces the transfer speed or temporarily stops the transfer. It will stop.

According to this invention, the compression means uniformly compresses without dividing the pixels, checks the number of output pixels already sent to the image output unit, and compares the number of output pixels with one area of the storage means. When the number of pixels of the decompressed data already stored in the memory is large, the transfer control means slows down or temporarily stops the transfer, and executes the transfer when the number of pixels is less than that. It is possible to avoid overflow of pixels in the data storage area before being sent to the output unit.

Further, the image processing apparatus according to claim 5 further comprises a compression ratio adjusting means for adjusting a compression ratio of the image compression means in accordance with a transfer speed.

According to the present invention, when the compression ratio is low, for example, an abnormal image in which data to be output by the image output unit can be obtained because data is not sufficiently transferred to the storage unit may occur. By means, the compression ratio is adjusted so as to achieve the required transfer rate.

Further, in the image processing apparatus according to the present invention, the image compression means and the image decompression means may include:
Image information is compressed and decompressed in accordance with an encoding / decoding method in which code data and decoded data have a fixed length.

According to the present invention, for example, GBTC
By employing a fixed-length compression / decompression method such as a (block truncation) type encoding method, it is possible to easily calculate the decompressed code length from the compressed code length.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an image processing apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. The present invention is not limited by the embodiment.

In this embodiment, 1200 dpi (do
t per inch) and a laser printer that writes one bit of four colors of C (cyan), M (magenta), Y (yellow), and K (black) as an example. It is assumed that output is requested at a speed of one sheet per second.

(Embodiment 1) FIG. 1 is a block diagram showing a schematic configuration of a laser printer according to Embodiment 1 of the present invention. The laser printer (hereinafter, referred to as a printer) 10 is connected to a host computer 20 and is represented by functional blocks centered on the image processing apparatus.
The printer 10 includes a page creation buffer 11, a page memory 12, an output unit 13, a shared bus 14, a compression unit 15, a compression ratio adjustment unit 16, a transfer control unit 17, a decompression unit 18, a temporary A storage buffer 19.

The page creation buffer 11 outputs (writes) data received from the host computer 20.
It is provided to perform a work of converting the image data into a suitable image data. More specifically, if the data sent from the host computer 20 is expressed in a page description language such as PostScript (a computer language developed by Adobe in the United States), it is stored in the page creation buffer 1.
1 is converted to bitmap data.

The compression section 15 compresses the created bitmap data. Various known techniques are known as compression methods. In particular, as a binary compression method, run length encoding (MH encoding, MR encoding) in which a run length in which black / white pixels continue in the scanning line direction is represented by a variable length code, or a binary image is highly efficient. The JBIG standard (Joint Bi-level Image Coding Experts Gruup), which is an international standard method for encoding, is known, such as Reference: Basic Technology of International Standard Image Coding (First Edition by Fumitaka Ono), Corona Publishing, p. I have. Which compression method to use may be appropriately selected according to the compression ratio. In this embodiment, the JBIG standard is used.

The feature of JBIG is to create an image pyramid to enable stepwise transmission,
That is, the reduced images having a small number of pixels are sequentially transmitted. J
In BIG, since the target is a binary image, a reduced image is generally created by a logical expression from a plurality of pixels. That is, a PRES (Progressive Reduction Scheme) method is employed as an image reduction method using a hierarchical coding method.

The decompression unit 18 decompresses the compressed data compressed by the compression unit 15 into bitmap data again. In this embodiment, the decompressed bitmap data is basically the same as the bitmap data before compression because the JBIG standard, which is lossless compression, is used. However, adjustment is performed by the compression ratio adjustment unit 16 described later. If it does, the data will be degraded.

The page memory 12 has a storage capacity for bitmap data of at least one page (A3 size in this example). In order to perform high-speed recording in a laser printer or the like, the page memory 12 needs to transfer the bitmap data to the output unit 13 in a short time in page units. However, the host computer 20
Since the communication speed between the printer and the printer 10 is generally low, the data is converted into bitmap data each time it is received from the host computer 20 and sent to the output unit 13, so that the output does not match the output. For this purpose, a page memory 12 is provided.

The output unit 13 actually prints out image data on recording paper. In this embodiment, an image forming method using an electrophotographic process by laser writing is adopted. The image data sent to the output unit 13 is CMY
It is assumed that the colors are sent in the order of K, page by page (sequentially).

In addition to the above-mentioned reason for the necessity of the page memory 12, the second and subsequent pages are output directly from the page memory 12 to the output section 13 when a plurality of copies of the same page are output. The purpose is to improve the output throughput. Here, as the page memory 12, DRA
M (Dynamic RAM), SRAM (Static R
AM) or a semiconductor memory (eg, a RAM disk, a silicon disk, a semiconductor disk, etc.) or an HD
D (hard disk), or semiconductor memory and HDD
And a storage device that combines the above.

It is preferable that the capacity of the page memory 12 be small in order to reduce the memory cost at a low price. Therefore, in this embodiment, since the data stored in the page memory 12 is compressed small-capacity data,
The capacity of the page memory 12 can be remarkably saved (effectively used).

The temporary storage buffer 19 stores the bitmap data after the decompression processing, and is provided to stably supply the expanded bitmap data to the output unit 13. That is, since the number of pixels of bitmap data expanded from a compressed signal cannot be generally predicted in variable-length compression, the number of pixels obtained in a unit time on the expansion side fluctuates drastically due to the nature of the image to be compressed. I do. Therefore, a temporary storage buffer 19, which is a means for storing decompressed data, is provided. By controlling the state in which a fixed number of pixels or more is always stored in the temporary storage buffer 19 at the time of writing, the output unit 13 Stable supply of bitmap data.

Here, as the temporary storage buffer 19, 1
Although it is possible to prepare a capacity for a page, the data amount for one page of A3 size is as large as 139.2 MB. Therefore, in consideration of economy, in this embodiment, 20 lines of one color are used. Prepare a buffer area for Furthermore, in this embodiment, in particular, the temporary storage buffer 19 is divided into two data storage areas 19a and 19b by 10 lines by address operation as shown in FIG. Shall be.

That is, as shown in the timing chart of FIG. 2, while the currently expanded bitmap data is stored in one area (hereinafter, data storage area A),
At the same time, in the other area (hereinafter referred to as data read area B), the stored bitmap data is sent to the output unit 13 for writing, and the start address of each area is sequentially exchanged to alternate the role of each area. Switch to

The transfer control unit 17 includes a temporary storage buffer 19
In order to instruct the page memory 12 to start / stop the transfer in accordance with the situation described above, and to control the addresses of two areas (see FIG. 3) of the temporary storage buffer 19.
In this embodiment, the above-described PCI bus is used as the shared bus 14.

Next, the operation of the printer configured as described above will be described. FIG. 4 is a flowchart illustrating an operation example at the time of output (at the time of reading) according to the embodiment of the present invention. At the time of output, first, compressed data of a corresponding color is read from the page memory 12 (step 11). That is, the compressed data for one page of the C (cyan) color is read from the page memory 12, and the shared bus (PCI bus)
It is sent to the extension unit 18 via. Subsequently, the extension unit 18
Is compressed by hierarchical coding in accordance with the JBIG standard in this example, the compressed data is decompressed from hierarchically low-resolution images and sequentially decompressed by hierarchical coding in which high-resolution images are sequentially replaced (step S12). The temporary storage buffer 19 stores the expanded bitmap data in the data storage area 19a (Step S13).

The transfer control section 17 has a data storage area 19a.
It is determined whether or not the bitmap data stored in the memory has reached 10 lines (step S14). Here, the bitmap data stored in the data storage area 19a is 1
If it is determined that the data has reached 0 lines, it is further determined whether or not all the bitmap data of the previous 10 lines stored in the data read area 19b have been sent to the output unit 13 (step S15). Here, if it is determined that all the previous 10 lines have been output, the two regions 19a and 19b
Are switched (step S16).

By the above switching, the data storage area 19a and the data read area 19b of the temporary accumulation buffer 19
(See FIG. 3), the operation of newly outputting 10 lines of bitmap data to the output unit 13 is repeated, and it is determined whether the transfer of A3 size and one page has been completed (step S17). . Then, when the data of the corresponding color reaches one page of A3 size, image formation of the color is executed (step S18). That is, based on the electrophotographic process, a latent image is formed by performing laser writing on the photoreceptor, and through an image forming process such as development and transfer,
The output of the C color is completed.

After the formation of the C color image, the reading of the next color data is determined (step S19). That is, after C color, M (magenta), Y (yellow), K
The processing of the next color is performed in order of (black). in this case,
Since the next color is M (magenta), the M color compressed data is read from the page memory 12, and the same processing is performed.
The output of the color image of one page of three sizes is completed.

As described above, in the first embodiment, since the data passing through the shared bus 14 using the PCI bus is data compressed by the compression unit 15, the transfer capability of the shared bus 14 ( Regardless of the limit, data can be transferred at high speed. For example, assuming that the transfer speed of the PCI bus is 66.5 MB / sec, which is 50% of the maximum performance, in order to output information of 139.2 MB of A3 color image one sheet per second, the bitmap data needs to be 1 bit.
What is necessary is just to compress to a compression ratio of 39.2 / 66.5 = 2.1.

In consideration of a case where a high-speed output is required in the future, for example, when the required throughput is required to be two sheets per second, the compression having a compression ratio of 4.2 or more may be performed. There is an advantage that there is no need to make any changes to the configuration centering on the PCI bus.

By the way, in this embodiment, as shown in FIG.
The expanded data can be stored only for the line. Therefore, if the number of expanded bitmaps exceeds 10 lines, a memory overflow occurs. Such an overflow is considered to occur with a high probability when a compression method such as a run length in which one code represents a large number of pieces of pixel information is used.

Therefore, in consideration of the case where such an overflow occurs, the compression unit 15 divides the image data into a plurality of regions every 10 lines, and performs compression in units of the image data of 10 lines. Then, at the time of compression transfer, the transfer control unit 17 receives the signal from the temporary storage buffer 19 indicating that the bitmap in the data storage area 19b has been sent to the output unit 13, and executes the following two processes.

That is, the transfer control unit 17 sends an instruction to transfer the next 10 lines of compressed data to the page memory 12 by a control signal, while switching the head address of each area to the temporary storage buffer 19. To indicate that Therefore, by adopting such a method, since the compressed data sent from the page memory 12 to the decompression unit 18 is always data for 10 lines of the C color, the data storage area of the temporary storage buffer 19 is prevented from overflowing. You.

On the other hand, since the compression ratio is low and the bitmap data is not sufficiently transferred to the temporary storage buffer 19, the bitmap data to be output by the output unit 13 cannot be obtained. As a result, an abnormal image occurs. Sometimes. In this case, it is conceivable that the high-speed output (one sheet per second) is abandoned and the operation is restarted from the beginning, while the output is performed by rotating the photoconductor drum slowly. I do. That is, the compression rate is adjusted to a compression rate higher than the compression rate necessary to achieve the required throughput.

In this embodiment, the transfer target 10
The compression ratio of the compressed data for the line is equal to the “compression ratio necessary to achieve the required throughput”, that is, in this embodiment, the compression ratio is 2.1 (the calculation method is the same as described above). If it is smaller, the compression ratio adjuster 16 adjusts the compression ratio so that the compression ratio becomes 2.1 times or more.

More specifically, since the compression unit 15 adopts the JBIG standard as a compression method, the compression unit 15
When the compression ratio of the image data for the line is less than 2.1, the compression ratio of 2.1 is achieved by using only the low-resolution layer as the compressed data. By adjusting the compression ratio, the compressed data in units of 10 lines compressed by the compression unit 15 is always adjusted to the compression ratio of 2.1 or more, so that it is possible to prevent the occurrence of an abnormal image due to the low compression ratio. .

Therefore, it is possible to cope with the case where the expanded bitmap data is larger or smaller than the capacity of the data storage area of the temporary storage buffer 19. Therefore, it is possible to completely cope with a problem inherent in transferring variable-length compressed data to the shared bus 14 in which the number of pixels of the decompressed data cannot be predicted, and to always output an image at a required speed. Can be.

Here, a comparison is made between the shared bus type architecture of the present invention shown in FIG. 1 and the conventional shared bus type architecture shown in FIG. Although the printer 1 in FIG. 9 has a portion having the same function as the printer 10 in FIG. 1, the upper limit of the transfer speed cannot exceed the maximum transfer speed of the PCI bus. It is necessary to change the shared bus or increase the bus width.

On the other hand, according to the present invention, even when the required transfer rate exceeds the maximum transfer rate of the PCI bus, the transfer rate can be substantially improved by data compression. It is possible to achieve the required transfer speed. For this reason, even when the required transfer speed changes depending on the model, it is not necessary to make a change such as exchanging the shared bus, so that there is a special effect that the merit of the architecture centering on the shared bus can be fully utilized.

(Embodiment 2) This embodiment 2 has a configuration in which the compression ratio adjusting section 11 is omitted from FIG. Therefore, each functional unit has the same function as that of the first embodiment, and is different in that the transfer control unit 17 performs a process described later in order to prevent the temporary storage buffer 19 from overflowing. FIG. 5 is a flowchart illustrating an operation example according to the second embodiment of the present invention.

Referring to FIG. 5, first, the compression unit 15 performs uniform compression without dividing pixels in predetermined units (step S21). On the other hand, the printer controller (not shown) checks the number of pixels (N) already sent to the output unit 13 from the data reading area (19b in FIG. 3) of the temporary storage buffer 19 at a predetermined timing (step S22). . Then, the above N obtained as a result of the check is set as a threshold value, and compared with the number of pixels (M) of the decompressed data already stored in the data storage area 19a (step S2).
3) It is determined whether or not M> N (step S2)
4).

If it is determined in step S24 that M> N, a signal is sent to the transfer control unit 17, and the transfer control unit 17 receiving the signal sends a control signal to the page memory 12 to temporarily stop the transfer. Send (step S25).
Subsequently, it is determined whether or not N> M (step S2).
6) If N> M, the printer controller sends a signal again, and the transfer control unit 17 receiving the signal sends a control signal to restart the transfer to the page memory 12 (step S27).

Therefore, according to the second embodiment,
Since the number M of pixels stored in the data storage area of the temporary storage buffer 19 is substantially equal to or less than the number N of pixels already output from the data output area, all pixels in the data output area are output to the output unit. It is avoided that the pixels in the data storage area overflow the storage capacity before being sent.

(Embodiment 3) FIG. 6 is a block diagram showing a schematic configuration of a laser printer according to Embodiment 3 of the present invention. The configuration shown in FIG. 6 is different from FIG. 1 of the first embodiment in that the compression unit 15 is connected to the shared bus 14 integrally with the page memory 12 instead of the page creation buffer 11. Therefore, since other components and their functions are the same as those in the first embodiment,
The same reference numerals as those in FIG. 1 denote the same parts, and a description thereof will be omitted.

In the third embodiment, when image data is transferred between the page creation buffer 11 and the compression section 15, the transfer speed cannot be higher than the transfer speed of the shared bus 14. When the image data is transferred from the memory 12 to the decompression unit 18, the compressed image data flows on the shared bus 14. Therefore, when printing the same page a plurality of times, the transfer speed of the shared bus 14 is a bottleneck. , A high-throughput can be achieved without increasing the speed of the first print, and a basic configuration change is required to improve the required transfer speed, similarly to the first embodiment. Can be dealt with without performing.

(Embodiment 4) FIG. 7 is a block diagram showing a schematic configuration of a copying machine according to Embodiment 4 of the present invention. This copier 30 has a configuration in which a scanner 21 is added to the above-described configuration of the printer 10 in FIG. Instead, an expansion unit 24 for decoding (expanding) the data compressed by the compression unit 23 is provided. Therefore, the other components and their functions are the same as those in the first embodiment, and thus the same reference numerals as those in FIG. 1 are used and the description thereof is omitted.

Here, in the fourth embodiment, the output unit 1
No. 3 performs 8-bit multi-level writing. Therefore, the compression unit 23 also needs to compress an image having a depth of 8 bits. In this example, the compression unit 23 employs a fixed length compression method. Various systems are known as fixed-length compression systems. In the fourth embodiment, however, GBTC is used.
(Generalized block truncation coding). The details of GBTC are disclosed in, for example, Japanese Patent Application Laid-Open No. 6-164950. GBTC
Is a type of block encoding method in which pixel information of a 4 × 4 block is decomposed into a gradation component and a resolution component, and these components are encoded. The outline is described below for reference.

For example, an image is decomposed into blocks of 4 × 4 pixels and classified into the following three modes according to the dynamic range of the gradation difference in the block (the difference between the maximum value and the minimum value of the pixels in the block). . Each block is decomposed into level designation information (2-bit signals: Φ ₁ , Φ ₂ ) for specifying a quantization level for each pixel, a reference level (L _a ) for specifying a quantization level, and _a level interval (L _d ). .

Mode A: When the gradation difference is very small,
Quantized in each pixel 1 level (average value L _a of the block). Mode B: when the gradation difference is slightly larger, each of the representative values of the two levels (dark pixel group than the median of the block and light pixel group within the tone distribution in a block of pixels, i.e. L _a + L _d / 2 and L _a −L _d / 2 Mode C: When the gradation difference is very large, each pixel is divided into four levels within the range of the gradation distribution in the block (the gradation distribution in the block). equally spaced within the range, i.e. L _a + L _d / 4 and L
Quantize to _a− L _d / 4.

The quantization of the blocks belonging to the mode C is performed, for example, as follows. First, the L _a information encoded transmission. At this point, the decompression side can reproduce a rough image in which all blocks are expressed at one level. Then the L _a information and [Phi ₁ information coded transmission. At this point, since the blocks in modes B and C are displayed in two gradations, the image quality of the expanded image is improved. Finally Φ
₂ is encoded and transmitted. At this point, the block of C is expressed in four gradations, and the reproduced image becomes a clearer image.

In FIG. 7, the image data is read for each color by the scanner 21 performing four scans. The image data is compressed by the compression unit 23 and stored in the page memory 12 only when copying a plurality of copies. The compressed data is transmitted to the decompression unit 2 via the shared bus 14.
4 for reproduction and output by the decoding process.

The compression unit 23 performs the fixed-length compression based on the GBTC described above. In the case of fixed length compression, the code length after decompression can be easily calculated from the code length after compression, so that the data amount of decompressed data can be predicted. Therefore, by performing this prediction, it is possible to avoid the situation where the temporary storage buffer 19 overflows or the transfer is not in time. Therefore, the fourth embodiment has an advantage that complicated transfer control is not required.

By the way, in addition to the above-described embodiment, a compression unit for storing in the page memory 12 is provided by the shared bus 1.
4 may be provided separately from the compression unit 15.
In the printer 10, the host computer 2
If the communication between the printer 0 and the printer is sufficiently fast, the page creation buffer 11 may be provided in the host computer 20, or both the page creation buffer 11 and the compression unit 15 may be provided in the host computer 20. You may.

In this embodiment, the shared bus 14
However, the present invention is not limited to this. In addition, as an image forming method of the output unit 13, an electrophotographic method using laser writing has been described as an example. However, in addition to this method, a thermal transfer (thermal) method, an inkjet method, or the like may be used.

Here, the terms related to the above-described embodiments will be supplementarily described. First, as a compression method, variable length compression (in this example, JBIG) and fixed length compression (in this example, GBTC) are appropriately selected and used. Variable-length compression is preferable from the viewpoint of high-speed transfer because the compression ratio is high, and fixed-length compression is preferable because the number of pixels obtained on the decompression side is stable.

Image compression is lossless compression (lossless encoding).
Irreversible compression (irreversible encoding) may be used, but lossless compression is preferable because the original image can be restored and there is no deterioration in image quality. (Encoding efficiency) is high. Here, in the case of lossless compression, the image data and the decompressed data in the present invention match. Further, the image data may be bitmap data or data expressed in a page description language (PDL) or the like. The means for inputting image data may be a document reading device such as a scanner or a means for receiving data transferred from a host computer or the like via a network or the like.

The temporary storage buffer 19 (storage means)
It is preferable to provide a capacity capable of storing one page of decompressed data, since a stable output can be obtained. However, if a capacity capable of storing only a part of the decompressed data is provided, the memory size is reduced, and the cost reduction is achieved. Is preferred. Further, from the processing side, it is desirable that the plurality of regions (see FIG. 3) be bands composed of a plurality of lines.

The compression ratio indicates a value obtained by dividing the data amount before compression by the data amount after compression. Also, the throughput is
It means the number of pages output per unit time. For example, the compression ratio required to achieve the required throughput is a compression ratio required for the image processing device and required to achieve the throughput, and it is assumed that stable transfer is possible. The transfer speed of the shared bus is V (sheets / sec), and the number of sheets to be output per second is M (sheets / s).
ec), it is represented by M / N.

The compression ratio adjusting section 16 may be a means for quantizing, a means for reducing the resolution, a means for selecting any of a plurality of compressed data, and the like.
Adjustment of the compression ratio may be performed in the compression unit at the time of compression, or may be performed by providing a quantizing unit immediately before transferring the compressed data via the shared bus. It is preferable to do it sometimes.

[0076]

As described above, according to the image processing apparatus of the present invention (claim 1), image information to be subjected to image processing (output) is compressed according to a compression method predetermined by the image compression means. Since the data is generated, and the compressed data is supplied to the image decompression means via the shared bus and decoded there, the apparent transfer speed of the shared bus is improved, and the transfer speed of the shared bus is a processing bottleneck. Can be avoided, and even if a transfer speed exceeding the transfer speed limit of the shared bus is required, compressed data that can be transferred with the transfer capacity of the shared bus or less passes through the shared bus. It is possible to respond without changing the central basic configuration.

According to the image processing apparatus of the present invention (claim 2), image information to be subjected to image processing (output) is
The compressed data is converted into compressed data according to a compression method predetermined by the image compressing means, and the compressed data is stored in the compressed data storing means, for example, in page units, and the compressed data is transmitted from the compressed data storing means to the image decompressing means via the shared bus. By supplying the data, it is possible to repeatedly read the compressed data for the page, so that when printing the same page a plurality of times, it is possible to cope with a transfer speed exceeding the transfer limit of the shared bus.

According to the image processing apparatus of the present invention, the next predetermined unit of the next predetermined unit is stored in the page memory based on the signal indicating that the predetermined amount of decompressed data has been output from the storage means. Instruct the transfer of compressed data (number of pixels),
By alternately switching the plurality of areas of the storage means to the storage area / readout area, the upper limit of the number of pixels at the time of decompression is determined, so that overflow of the memory can be prevented.

According to the image processing apparatus of the present invention, the compression means uniformly compresses the image without dividing the pixels, and checks the number of output pixels already sent to the image output unit. When the number of pixels of decompressed data already stored in one area of the storage means for the number of output pixels is large,
The transfer control means slows down or suspends the transfer, and restarts the transfer if it is less than that. Therefore, the overflow of pixels in the data storage area before all the pixels in the data output area are sent to the image output unit. Can be avoided.

Further, according to the image processing apparatus of the present invention (claim 5), for example, when the compression ratio is low, the data to be output by the image output unit is obtained because the data is not sufficiently transferred to the storage means. In consideration of the occurrence of an abnormal image, the compression ratio is adjusted by the compression ratio adjusting means to a predetermined value so as to achieve the required transfer speed. Therefore, it is possible to prevent the occurrence of an abnormal image due to a low compression ratio. it can.

According to the image processing apparatus of the present invention (claim 6), for example, by adopting a fixed length compression / decompression method such as a GBTC (block truncation) type encoding method, a code after compression can be obtained. The length of the decompressed code can be easily calculated from the length, and the data amount of the decompressed data can be predicted. Therefore, it is possible to prevent the memory from overflowing and to prevent the transfer from being performed in time. Can be avoided.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a laser printer according to a first embodiment of the present invention.

FIG. 2 is a time chart schematically showing a method for controlling two areas of the buffer according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating a state of two areas of the buffer according to the first embodiment of the present invention;

FIG. 4 is a flowchart illustrating an operation example at the time of output (at the time of reading) according to the first exemplary embodiment of the present invention;

FIG. 5 is a flowchart illustrating an operation example according to the second exemplary embodiment of the present invention;

FIG. 6 is a block diagram illustrating a schematic configuration of a laser printer according to a third embodiment of the present invention.

FIG. 7 is a block diagram illustrating a schematic configuration of a copying machine according to a fourth embodiment of the present invention;

FIG. 8 is a block diagram showing a system configuration of a conventional digital copying machine using a shared bus.

FIG. 9 is a block diagram showing a schematic configuration of a conventional system based on a shared bus architecture.

[Explanation of symbols]

 Reference Signs List 10 printer 11 page creation buffer 12 page memory 13 output unit 14 shared buffer 15, 23 compression unit 16 compression ratio adjustment unit 17 transfer control unit 18 decompression unit 19 temporary storage buffer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H03M 7/46 H03M 7/46 (72) Inventor Hiroaki Suzuki 1-3-3 Nakamagome, Ota-ku, Tokyo No. 6 Inside Ricoh Co., Ltd. (72) Inventor Yukiko Yamazaki 1-3-6 Nakamagome, Ota-ku, Tokyo F-term inside Ricoh Co., Ltd. CC08 DD13 5C073 AA01 AA02 BB09 BC02 CE01 5C078 BA21 CA27 CA35 5J064 AA03 BA08 BC01 BD00

Claims (6)

[Claims] 1. An image processing apparatus for transferring input image information to an image output unit via a shared bus, comprising: an image compression unit for compressing the image information to generate compressed data; An image processing apparatus, comprising: image decompression means for generating data; and transferring compressed data to the image decompression means via the shared bus. 2. The image processing apparatus according to claim 1, further comprising a compressed data storage unit that stores the compressed data and outputs the compressed data to the shared bus, wherein the image decompression unit decompresses the compressed data from the compressed data storage unit. The image processing device according to claim 1. 3. A storage unit having a plurality of areas divided for each predetermined storage capacity and storing decompressed data in the area, and outputting a predetermined amount of decompressed data from the storage means. Transfer control means for instructing the transfer of the next predetermined unit of compressed data based on a signal indicating, and alternately switching a plurality of areas of the storage means to a storage area / readout area, respectively. The image processing apparatus according to claim 1, wherein: 4. The transfer control unit according to claim 3, wherein the transfer control unit speeds down or temporarily stops the transfer when the decompressed data stored in the storage unit exceeds a predetermined number of pixels. Image processing device. 5. The compression ratio of the image compression means,
The image processing apparatus according to any one of claims 1 to 4, further comprising a compression ratio adjusting unit that adjusts according to a transfer speed. 6. The image compression means and the image decompression means for compressing and decompressing image information in accordance with an encoding / decoding method in which code data and decoded data have a fixed length. Or the image processing device according to 2.