KR950011196B1 - Image data compressing and decompressing apparatus - Google Patents

Abstract

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Description

Image data compression extension device

1 is a facsimile apparatus using the image data compression and expansion apparatus of the present invention.

2 is an enlarged view of the main part of the image data compression extension apparatus.

3 is a diagram for explaining the structure of a buffer memory.

4 is a diagram illustrating a process of using a buffer memory.

5 is a diagram for explaining calculation of a required capacity of a buffer memory.

6 is a view showing a print path when a reduction circuit is added.

7 is a diagram for explaining a buffer memory and a page memory.

8 is a facsimile apparatus using the first conventional example of the image data compression and expansion apparatus.

9 is a facsimile apparatus using a second conventional example of an image data compression and expansion apparatus.

10 is a view for explaining the reason for using an image reading unit and an image recording unit operating intermittently, which is an image data compression and stretching apparatus of the first conventional example.

Fig. 11 is a diagram showing a path through which data flows during various operations in the image data compression and expansion apparatus.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an image data compression stretching apparatus used in a facsimile apparatus or the like.

The image data compression / extension device is an apparatus for compressing an image obtained by reading an image to code data by encoding or conversely extending the code data to image data by decoding, and is used in a facsimile apparatus or the like.

[First Conventional Example]

Intermittent operation method using buffer memory

8 is a facsimile apparatus using the first conventional example of the image data compression and expansion apparatus. 8, 1 is an image reading unit, 2 is an image recording unit, 3 is a buffer memory control circuit, 4 is a buffer memory, 5 is a compression extension unit, 6 is a code memory unit, 7 is an operation panel, and 8 is a CPU (center). Arithmetic processing unit), 9 is ROM (lead only memory), 10 is RAM (random access memory), 11 is modem, 12 is line control unit, 13 is communication line, 14 is bus, 19 is input image data A control circuit, 20 is an image data output control circuit, and 22 is an image data compression and expansion device.

The image data input circuit 19 controls when writing the image data from the image reading unit 1 into the buffer memory 4, and the image data output control circuit 20 transfers the image data to the image recording unit 2. In order to read the image data from the buffer memory 4, control is performed.

The main operations performed by the image data compression and expansion device 22 are 1) image reading operation 2) printing operation and 3) copying operation. 11 shows a path through which data flows when performing these operations.

11A shows a path through which data flows in the image reading operation. The image reading unit 1 reads the image of the original to generate image data, and stores it in the buffer memory 4 once. Next, the image data is taken out from the buffer memory 4, encoded (coded) by the compressed expansion unit 5, and converted into code data.

The time required for encoding depends on the degree of complexity of the image. For example, if the part of the beck is continuous, it ends in a short time, and the more the mixing degree of white and black becomes, the longer the time becomes.

The so-called "one bit ladder" in which white and black alternately appear every bit requires the longest time. The coded code data is stored in the code memory section 6. The code memory unit 6 is composed of, for example, DRAM (dynamic random access memory).

When the code data stored in the code storage unit 6 is transmitted to another facsimile device, the code storage unit 6 is transferred from the code storage unit 6 to the modem 11 to the line control unit 12 to the communication line 13. It is recorded in the code memory section 6 in the facsimile apparatus.

11B shows a path through which data flows in the printing operation. The printing operation is performed when code data has been transmitted from another fax machine. The code data of the code storage section 6 is transmitted to the compressed expansion section 5, decoded, and converted into image data. The image data is once stored in the buffer memory 4 and then transferred to the image recording section 2 for printing.

11C shows a path through which data flows in the copy operation. The original is read by the image reading unit 1, and the generated image data is once stored in the buffer memory 4, and then transferred to the image recording unit 2 for printing.

The operation panel 7 is a panel for the operator to issue various operation commands. The ROM 9 stores programs of operations performed in the COU 8. The RAM 10 provides a work area required when the CPU 8 performs an operation.

However, the capacity of the buffer memory 4 is usually very small compared to the amount of image data for one page of an original. 7 is a diagram for explaining a buffer memory and a page memory. FIG. 7A shows a page 17 of an original, FIG. 7B shows a page memory 16 capable of storing all the image data of the original 17, and FIG. 7C shows a buffer memory 4. FIG. The buffer memory 4 can store only the image data of the image of the solid line portion, for example, only a part of the document 17, but cannot store the image data of the dotted line portion. This causes the image reading unit 1 and the image recording unit 2 to use an intermittent operation as described below.

FIG. 10 is a diagram for explaining the reason why an image reading unit and an image recording unit operating intermittently in the image data compression and stretching apparatus of the first conventional example are used. In Fig. 10, 4-1 is a use portion, 4-3 is an overlap portion, 18 is a printing paper, 18-1, 18-3 is a printing portion, and 18-2 is a non-printing portion. FIG. 10A shows a print state on the print paper 18 during the print operation, and FIG. 10B shows a use state of the buffer memory 4 during the read operation.

The buffer memory 4 is used as a ring buffer when the address value is increased to become the last address, and then the first address is specified.

Therefore, in the state of reading until the buffer memory 4 is full during the image reading operation and continuing the reading, new image data is overlapped and written on the previously read image data (overlap portion 4 in FIG. 10B). 3).

In this case, the previous image data is deleted while not in use.

Since it is not necessary to do so, the reading operation of the image reading unit 1 is once stopped. After the image data of the buffer memory 4 is encoded and terminated by the compression extension unit 5, the reading operation of the image reading unit 1 is resumed at the previously stopped position. Therefore, as the image reading unit 1, an image scanner capable of intermittently reading an image should be used.

In the printing operation, only a part of one page of image data is stored in the buffer memory 4 via the compression storage section 5 by the code storage section 6. Image data of the buffer memory 4 is transferred to the image recording unit 2 at a constant speed. However, since the speed of decoding in the compression extension section 5 depends on the complexity of the image, it is not transmitted at a constant speed from the compression extension section 5 to the buffer memory 4. Therefore, the buffer memory 4 may be left blank. If the image recording unit 2 continues to operate in this state, a blank portion is formed on the printing paper (non-printing unit 18-2 in Fig. 10A), and the image is cut off on the way.

This is not so good. When the buffer memory 4 becomes empty, the printing operation of the image recording unit 2 is once stopped and resumed after the next image data arrives in the buffer memory 4. Therefore, as the image recording unit 2, a printer or a dot printer or the like at the time of intermittent printing capable of intermittently printing is used.

Second Conventional Example

Continuous operation method using page memory

In the first conventional example described above, since the image reading unit 1 and the image recording unit 2 operate intermittently, there is a drawback that the reading time or the printing time is long. Therefore, there is something that can operate continuously without being intermittent.

9 shows a facsimile apparatus using the second conventional example of the image data compression and expansion apparatus. Reference numerals correspond to those in FIG. 15 is a page memory control unit, and 16 is a page memory. The capacity of the page memory 16 is about the size of A3 and requires about 4M bytes when the binary data having a dot density of 400 dpi (dot per inch) is targeted. Since the operation of the constituent elements as in the eighth diagram is the same as in the case of the first conventional example, the description thereof will be omitted. However, as the image reading unit 1, an image scanner that can operate continuously is used, and as the image recording unit 2, a printer that continuously operates, for example, a laser beam printer, is used. These perform a read operation, a print operation, or the like at a constant speed determined by each model.

The page memory 16 has a capacity for storing image data of one page of an original as shown in FIG. 7B. Therefore, when reading or printing one page of an original, the page memory 16 reads or prints on the way. There is no need to stop. Therefore, the entire time required for reading or printing is shortened, thereby speeding up.

Moreover, as a conventional document related to an image data compression expansion apparatus, for example, Unexamined-Japanese-Patent No. 60-140975, Unexamined-Japanese-Patent No. 64-36461, Unexamined-Japanese-Patent No. 62-126430, Unexamined-Japanese-Patent No. 63-267060, It is publication 64-44678 publications.

However, the page memory used in the second conventional example as described above is expensive because it requires a large number of memory elements and has a problem of increasing the cost of the image data compression and expansion device. This invention makes it a subject to solve such a problem.

That is, an object of the present invention is to provide an image data compression / expansion device capable of continuously operating one or both of the image reading unit and the image recording unit even when a buffer memory composed of fewer memory elements than the page memory is used. It is done.

In order to solve the above problems, in the present invention, the configuration of the image data compression extension apparatus is used for the temporary storage of the image reading unit which operates continuously and / or the image recording unit which operates continuously, the compression extension unit, and the image data. And a code memory unit for storing code data obtained by compression by the compression extension unit. The capacity of the buffer memory unit is the capacity of the code memory unit, the worst compression ratio in the coding scheme employing the buffer memory, and the image recording unit. Alternatively, the data transfer rate between the image reading unit and the compression expansion unit and the buffer memory is determined based on the ratio of the data transfer rate.

In addition, an image recording unit for continuously operating an image data stretching device, a buffer memory having a capacity for sending out one page of original image data without interruption during a recording operation of the image recording unit, and image data in this buffer memory. A buffer memory control circuit that controls the buffer memory in the direction of flow so that the buffer memory does not become an amplifier even when extending the supplying section and the code data that takes the longest time to decompress when the decompression unit performs the decompression operation. It was set as having a configuration.

An image reading unit for continuously operating an image data compression device, a buffer memory having a capacity to be sent without erasing image data of one page of an original during a reading operation of the image reading unit, and a buffer memory Even when compressing a compression unit receiving image data and code data that takes the most time in compression when performing compression operation with this compression unit, the buffer memory is directed to the amplifier so that the buffer memory does not flow. The configuration has a buffer memory control circuit for controlling by the controller.

In the present invention, the capacity of the code storage unit is C, the worst compression ratio in the coding scheme employed is K, and the data transfer rate between the compressed expansion unit and the buffer memory for the data transfer rate between the buffer memory and the image recording unit or the image reading unit. When the ratio is P, buffer memory capacity Y

To satisfy the relationship

In this way, during compression, the image data continuously transmitted to the buffer memory at a constant speed can be processed by the image reading unit operating continuously, without causing the buffer memory to flow. At the time of decompression, image data must be sent from the buffer memory to a continuously operating image recording unit at a constant speed, but this can be done without the buffer memory becoming an amp.

The capacity Y can be made smaller than the capacity of the page memory by adjusting the values of C and P, so that the cost can be reduced.

EXAMPLE

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 is a facsimile apparatus using the image data compression and expansion apparatus of the present invention. Reference numerals correspond to those in FIG. As the image reading unit 1 and the image recording unit 2, those which operate continuously are used.

2 is an enlarged view of the main part of the image data compression and stretching apparatus of the present invention. 3-1 is a memory usage counter, 3-2 is a memory usage determination circuit, 3-3 is a frame width register, 3-4 is an address register, and 3-7 is a 3- 3 code. 9 is an address counter, DRE Q 1 to 3 is a data request signal, ACK 1 to 3 is an acknowledgment signal, and L _E and L _E 1 to 3 are line and signal.

3 is a diagram for explaining the structure of the buffer memory 4. As shown in FIG. 3A shows that the address of the buffer memory 4 is set in word units. In this example, one word is composed of 16 bits from 0 to 15. The buffer memory 4 is used as a ring buffer. That is, when the address is to be advanced after the last address Z, addressing is performed so as to return to the first address 0.

3B shows the capacity of the buffer memory 4 in that the length of one line (this is called "frame width") is W word. The head address of line 1 on the back side is W and the head address of line 2 is 2W.

In the case of an original having a large frame width W, the number of lines that can be stored is small. In contrast, in the case of an original having a small frame width W, the number of lines that can be stored is large.

4 is a diagram for explaining a process of using a buffer memory during expansion. 4-1 is a use section, 4-2 is a blank section, L _R is a read line (a line for reading), and L _W is a write line (a line for writing). 4 (a) shows the state before use, _and neither the read line L _R nor the write line L _W is included in the first line.

4B shows a state in which image data is being written. The write line L _W runs in the direction of the arrow _and reaches near the last line of the buffer memory 4. Readout is not yet disclosed, and readline L _R is not yet on the first line. The part where the dot was taken is the use part 4-1, and the blank part is the blank part 4-2. Since the buffer memory 4 is used as a ring buffer, when writing to the last line, the buffer memory 4 returns to the first line and then writes.

4C shows a state in which writing and reading are performed. The read line L _R starts at the first line and proceeds to near the final line. The writing line L _W returns to the first line from the last line and writes in such a manner as to write on the image data after the reading is completed. Therefore, the use section 4-1 and the blank section 4-2 of the memory are as shown.

The memory usage counter 3-1 in FIG. 2 is a counter that counts the number of image data lines that have not been read yet, that is, the number of lines in the user section 4-1 in FIG. When the line-and-signal signal L _E that informs the buffer memory control circuit 3 that writing of one line has ended, the count is +1, and the line-and signal L _E that informs that the reading of one line has ended. ), The count becomes -1.

The memory usage judging circuit 3-2 determines whether the use section 4-1 is completely lost (empty) or the buffer memory 4 is full in the use section 4-1 (full). Is a circuit for determining. Specifically, the value of the memory usage counter 3-1 (that is, the number of lines of the use portion 4-1 in which the dot of FIG. 4 is taken) and the number of lines 0 or the maximum number of lines L _{MAX are} determined. Judgment is made by comparison. When the number of lines coincides with the number of lines 0, the amplifier signal E _m is output, and when the maximum number of lines L _MAX that can be stored in the buffer memory 4 is matched, the full signal Fu is output.

In the frame width register 3-3, a value of the frame width (number of words constituting one line of an image) is set. In this example, the value is set to W. For example, the number of bits in one line when reading a document having a width of a sheet of A3 in the 400dpi image reading unit 1 is 4864 bits. This frame width is 304 words when one word is 16 bits.

When the compression stretching unit 5 is subjected to a compression operation, it is desired that the buffer memory 4 be in a state close to the ampliquary so that there is enough room to accept even if image data is continuously sent from the image reading unit 1. On the other hand, during the decompression operation, it is preferable that the image data is sufficiently present in the buffer memory 4 (close to the flop) so that the image data sent to the image recording unit 2 is not interrupted.

Before describing what conditions the capacity of the buffer memory 4 must satisfy in order to realize the above state, the operation of the image data compression and expansion apparatus will be explained by dividing the image reading operation, the printing operation, and the copy operation. .

[Image reading operation]

This operation is an operation of storing the image data read by the image reading unit 1 in the buffer memory 4 once, then converting it into code data in the compression expansion unit 5 and storing it in the code storage unit 6. to be.

(1) The write operation from the image reading unit 1 to the buffer memory 4 first starts the compression extension unit 5, and attempts to start the compression operation. However, since the image data has not yet been read in the buffer memory 4, the amplifier signal Em is output from the memory usage determining circuit 3-2. When there is no image data to be subjected to the compression process, the compression operation becomes a standby state. When the image reading unit 1 is activated, image data is input to the image data input control circuit 19 in series by one bit in accordance with the synchronization signal.

The input of image data from the image data input control circuit 19 to the buffer memory 4 is performed in parallel in word units (for example, when one word is 16 bits, 16 bits are bundled). The input is made when the arc nal signal ACK 1 output in response to the data request signal DREQ (1) is received.

The address registers 3-4 and the address counters 3-7 are used when inputting from the image data input control circuit 19 to the buffer memory 4. The address register 3-4 indicates the address of the head of the line currently being written. For example, in the period in which the word belonging to the line 1 in FIG. 3B is being written, the address W is maintained. The address counter 3-7 shows the address of the word which is writing.

For example, when the second word is written from the beginning of the line 1 in Fig. 3B, it is +1 every time one word is written, which is W + 1. When the first word of the first line is written, the contents 0 of the address registers 3-4 are set to the address counters 3-7.

Every time a word is sent out for one line. The line and signal L _E 1 are output. By the line-and-signal L ₃ 1, the value of the address register 3-4 becomes a value obtained by adding the frame width W. FIG. For example, when the line 2 is finished, W is added to 2W to be 3W (W2 + W = 3W). The writing of one line of image data to the buffer memory 4 increases the memory usage in the buffer memory 4 by one line, so the line-and-signal L _E 1 is input to the memory usage counter 3-1. To make the count +1.

(2) When one line is written into the buffer memory 4 for the storage operation from the buffer memory 4 to the code memory 6, the amplifier signal Em disappears. When the amplifier signal Em disappears, the compression extension section 5 starts a compression operation. The image data of the buffer memory 4 is read out when the acknowledgment signal ACK 3 is output in response to the data request signal EREQ 3. Reading is done at the beginning of the first line. The read image data is compressed and stored in the code memory section 6. The address registers 3-6 indicate the head address of the line on which the read / write to the compressed extension section 5 is performed. The address counter 3-9 indicates the address of the word being read out to the compressed extension section 5. When reading the word at the head of the first line, the value 0 in the address register 3-6 is set in the address counter 3-9.

Each time one word is read, the value of the address counter 3-9 is +1. Each time the reading of one line is finished (that is, each time the line and signal L _E 3 is output), the frame width W is added to the value of the address register 3-6. When one line is read from the buffer memory 4, the image data of the line is finished, and the memory usage is reduced by one line. When the line-and-signal L _E 3 is input, the value of the memory usage counter 3-1 is -1.

[Print Action]

This operation converts the code data stored in the code storage section 6 into image data in the compression extension section 5, stores them in the buffer memory 4, sends them to the image recording section 2, and prints them. It is an operation.

(1) In the operation of writing from the code memory unit 6 to the buffer memory 4, the compression expansion unit 5 is started, and the code data of the code memory unit 6 is converted into image data, thereby converting the buffer memory ( Fill in 4). At the beginning of the line to write, the value of the address register 3-6 is set in the address counter 3-9. The address for writing image data is instructed by the address counter 3-9. Each time one word is written, the value of the address counter 3-9 is +1. When writing of one line is finished and the line and signal L _E 3 is output, the frame width W is added to the value of the address register 3-6, and the value of the memory usage counter 3-1 is +1. .

(2) The operation of reading from the buffer memory 4 to the image recording unit 2 increases the amount of memory used in the buffer memory 4 and outputs the full signal Fu, so that the image recording unit 2 is started. do. Further, image data is read out from the buffer memory 4 when the arc raw signal ACK 2 is output in response to the data request signal DREQ 2 from the image data output control circuit 20. FIG. The readout is performed in word units, but the image data output from the image data output control circuit 20 to the image recording unit 2 is performed in a series format in accordance with the synchronization signal.

When reading image data from the buffer memory 4 to the image data output control circuit 20, the value of the address register 3-5 is set in the address counter 3-8 at the head of the first line. The value of the address counter 3-8 is +1 for every word read. When the reading of one line is finished, the line-and-signal L _E 2 is output, the frame width W is added to the address register 3-5, and the value of the memory usage counter 3-1 is -1.

[Copy operation]

This operation is an operation in which image data read out from the image reading unit 1 is once stored in the buffer memory 4 and printed in the image recording unit 2. The operation of writing the image data read by the image reading unit 1 into the buffer memory 4 is the same as the operation described in the section [Image reading operation], and the image data of the buffer memory 4 is transferred to the image recording unit 2. The reading operation is the same as the operation described in the section [Printing operation].

In order to allow the above operation to continue for one page of the original without interruption, the buffer memory 4 should not be an ampli- fier during the decompression operation and not flow during the compression operation. . In view of this relationship, the present invention calculates the minimum capacity of the buffer memory 4. Next, the calculation example will be described.

[Calculation Example of Capacity of Buffer Memory 4]

5 is a diagram for explaining the calculation of the memory capacity required as the buffer memory 4, and the case of decompression will be described as an example. 17 is a manuscript, 17-1 is a white part, 17-2 is a worst compression picture part, 6-1 is a back code part, 6-2 is a worst compression picture code part, and 21 is a 1-bit ladder. 5A shows a path through which data flows in the printing operation. 5B shows the states of the code memory unit 6, the buffer memory 4, and the document 17 when the decompression operation is performed under the worst condition.

The worst compressed image portion 17-2 of the document 17 refers to an image portion having the worst compression ratio when read compression is performed by the image reading portion 1. Such an image portion is a one-bit ladder 21 which is an image in which white and black are alternately arranged every bit. Therefore, the worst compressed image part 17-2 is filled with the 1-bit ladder 21. As shown in FIG.

When the 1-bit ladder 21 is compressed by the MH method (Modified Huff-man method) used for the facsimile apparatus, the compression ratio is 1 / 4.5. In other words, when one bit of image data is compressed, 4.5 bits of code data is obtained. In this case, it is not shortened but rather long.

The back code part 6-1 is a part which stores the code data which compressed the image data of the back part 17-1, and the worst compressed image code 6-2 is the worst compressed image part 17-2. This section contains the code data compressed from the image data.

The capacity and transmission rate of data in each part of Fig. 5A are set as follows.

① Capacity of buffer memory 4. … … … … … … … … … … … … … … … … Y bytes

② capacity of the code memory 6. … … … … … … … … … … … … … … … … C byte

(3) Transfer rate (constant) from buffer memory 4 to image recording section 2. < … … … X bytes / S

(S… seconds)

④ transmission speed from code memory section 6 to compression extension section. … … … … … … nX bytes / S

(Where n is a positive integer, which indicates how many times the X is)

⑤ Stretching operation capability of the compression extension part 5. … … … … … … … … … … … … PX bytes / S

(However, p ... coefficient indicating how many times compared with X mentioned above)

When the code data of the code storage section 6 is converted into image data by the compression extension section 5 and sent out to the image recording section 2 via the buffer memory 4, data transfer for one page is continuously performed. Even if it is done, it is requested that the non-printing portion 18-2, as shown in Fig. 10A, be prevented from appearing on the printing paper. In order to do so, even if there is code data that takes the most time for the decompression processing in the compression extension unit 5, for example, the last data must be sent to the image recording unit 2 without the buffer memory 4 becoming blank. do. Therefore, assuming the worst condition having the highest possibility of producing a non-printed portion, and calculating the capacity of the buffer memory 4 which does not produce a non-printed portion even under such conditions, the following is calculated.

First, the worst condition will be described in FIG. 5B. The first condition that defines the worst condition is that the amount is enough to fill the buffer memory 4 if it is stretched and converted into image data as shown in the drawing, and the smallest area in the compressed state. The condition is that the code data corresponding to the image stored in the code storage section 6 exists at the head of the code storage section 6 only by using. Such an image is an image of a white. Therefore, the back code part 6-1 exists in the head of the code memory part 6. As shown in FIG.

The second condition that defines the worst condition is the worst compressed image code part (after the back code part 6-1) that stores the code data (the worst (minimum) compression rate) that takes the longest to perform the decompression process ( It is condition that 6-2) exists.

The transfer from the buffer memory 4 to the image recording section 2 is started when the buffer memory 4 is filled with image data (when the full signal Fu is output).

If the width of the document 17 is equal to the width of the sheet of A3, and this is read by the image reading unit 1 having a dot density of 400 dpi (dot per inch), the image data of one line is 4864 bits. Therefore, the next number of lines can be stored in the buffer memory 4 having the capacity Y bits.

Can be stored in the buffer memory (4) Next, the memory amount of the back code part 6-1 corresponding to the image data of the back line filled in the buffer memory 4 is obtained. In order to express one line of the back of image data of 4864 bits as code data, 44 bits are required in the MH method, so the memory amount (bite) of the back code section 6-1 is as follows.

Of back cord part 6-1 In this case, the memory capacity of the worst compressed image code section 6-2 is obtained by the following equation.

Of the worst compressed image code section 6-2 The value of the second term of this equation is less than 1K bytes when assuming Y = 1M bytes, so to simplify the calculation,

Memory capacity #C of the worst compressed image code section 6-2. … … … … … … … … … … … … (One)

Let's think about it as cool.

When the worst-case (minimum) compression ratio is K, the code data of the worst-compressed image code section 6-2 is extended so that the amount (byte) of image data generated is

Image data amount corresponding to worst compressed image code section 6-2 = KC... … … … … … … (2)

to be.

The total amount (byte) of image data generated by extending the code data between the back code section 6-1 and the worst compressed image code section 6-2 is Y + KC. After the image recording unit 2 is activated, reading is continuously performed at a constant speed X bytes / S in the buffer memory 4, so that the time T ₁ required to continuously read and finish the above-described total amount is It becomes as follows.

… … … … … … … … … … … … … … … … … … … … … … … … (3)

On the other hand, the transmission of the code data from the worst compressed image code part 6-2 to the compressed extension part 5 is continuously performed as soon as the transfer of the back code part 6-1 to the compressed extension part 5 is completed. All. The decompression of the code extension of the compression extension section 5 and the worst compressed image code section 6-2 starts from the same point as when the image recording section 2 started reading from the buffer memory 4. Since the transfer rate is PX bytes / S, the time T ₂ required until the transfer of the image data in which the worst compressed image code section 6-2 is extended to the buffer memory 4 is completed is as follows. .

… … … … … … … … … … … … … … … … … … … … … … … … … … (4)

In order to prevent the non-printing portion from occurring on the printing paper printed by the image recording portion 2, it is necessary to extend and end the code data of the worst-extruded image code portion 6-2 before the time T ₁ elapses. In other words,

T ₁ ≥T ₂ ... … … … … … … … … … … … … … … … … … … … … … … … … … … … … (5)

The relationship needs to be established. Substituting equations (3) and (4) into equation (5), the capacity (Y) of the buffer memory 4 is

… … … … … … … … … … … … … … … … … … … … … … … … (6)

Is calculated.

That is, when the value of K, C, P is set, if Y is set to a value satisfying Eq. (6), the image data read out even by using the continuous operation as the image reading section 1 and the image recording section 2 is used. Part of the image is lost or the printed image is not interrupted.

For example, if C = 1M bytes, P = 0.8, K = 1 / 4.5, then Y≥1M / 18 bytes. If, as in the conventional example of FIG. 9, the code data for one page of the original code memory 6 has been converted into image data, and stored in the page memory 16, it is about 4M in A3 size and 4000 dpi. Bytes are required, but the value of the capacity 1M / 18 bytes of the buffer memory 4 of the present invention is very small.

6 is a diagram showing a print path when a reduction circuit is added. The reduction circuit 23 is a circuit for reducing the size of the original to be read by the image reading unit 1 so as to match the size of the printing paper when the paper size of the document to be read is larger than that of the printing paper. The reduction is done by, for example, stripping out some of the data, using a simple method.

Since the thinning is performed, the speed at which the image data is supplied to the buffer memory 4 is slower than when the reduction circuit 23 is not inserted in between. If the supply speed is slow, the buffer memory 4 tends to be an amp. Therefore, if the same value as C, n, P, etc., the capacity of the buffer memory 4 is to be accommodated at first. Should be somewhat larger.

In the above example, it is assumed that the image reading unit 1 and the image recording unit 2 operate continuously, but either one may operate continuously. The present invention can also be applied to an image data stretching device that performs only the stretching operation, or can be applied to an image compression device that performs only the compression operation.

As described above, according to the image data compression and expansion device of the present invention, even if the image reading unit or the image recording unit is operated continuously, it is only necessary to provide a buffer memory having a much smaller capacity than the page memory. You can get off.

Claims (1)

An image reading unit (1) and an image recording unit (2) for continuously inputting / outputting image data, an image data input control circuit (19) and an image data output control circuit (20) for controlling input / output of image data continuously And a buffer memory 4 for storing the image data, a buffer memory control circuit 3 for inputting / outputting image data of the buffer memory 4, and image data output from the buffer memory as code data. In the image data compression and expansion device, which comprises a compression expansion unit 5 for encoding and a code storage unit 6 for storing the encoded data, the capacity Y of the buffer memory is determined by the following equation, Y≥kc (1 / p-1) (Where c is the capacity of the code memory unit, k is the worst compression rate in the coding scheme employed, and p is the data transfer rate between the compression extension unit and the buffer memory for the data transfer rate between the buffer memory and the image recording unit or the image reading unit). Is a memory usage counter 3-1 for counting the number of lines of the use section 4-1 of the buffer memory 4, and the lines of the use section 4-1. And a memory usage determining circuit (3-2) for determining whether the number is the minimum number or the maximum number of lines.