JP2003244448A - Encoding method and decoding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an encoding method in which image data having a background pattern can be well compressed even when the background pattern is less correlated with nearby image data in the case of compressing the image data. <P>SOLUTION: As the encoding method for encoding the image data for a plurality of pages, this method is provided with a first memory for storing image data on a page to be encoded, an encoding means for encoding the image data stored in the first memory and a second memory for storing image data on the previous page and the encoding means performs encoding while referring to the image data on the previous page stored in the second memory. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an encoding method and an encoding method for encoding image data of a plurality of pages having the same background pattern for compression and decoding the code.

[0002]

2. Description of the Related Art In the conventional compression technique, it is used that image data has a strong tendency to have the same pixel value as neighboring data such as left adjacent or upper adjacent, such as run length code or delta row code. Then, an encoding method is generally used in which neighboring image data in the same page are referred to and if they are the same, compression is performed.

When print data output by an application program that outputs characters or figures overlaid on a background pattern called wallpaper or texture is expanded into image data and printed, this image is used to reduce the data size. When compressing data, if the background pattern itself can be compressed well, it is easy to compress the entire image data well.

[0004]

However, in many cases, the background pattern itself cannot be compressed so much, and in such a case, it is not always easy to compress the entire image data well.

FIG. 10 is an example of such print data. In the prior art, the image data of the character portion can be compressed well, but the image data of the background pattern portion has an irregular pattern. , It cannot be compressed very well because the correlation with the neighboring image data is low. Since the background pattern generally has a large area, it occupies a large proportion in the entire page, and if the background pattern cannot be compressed well, the entire page cannot be compressed well either.

The present invention has been made in view of the above problems, and an object of the present invention is, when compressing image data having a background pattern, a background pattern having a low correlation with neighboring image data. Even so, an object of the present invention is to provide an encoding method that can be well compressed and a decoding method that decodes the code.

[0007]

To achieve the above object, the present invention provides a first memory for storing image data of a page to be encoded in an encoding method for encoding image data of a plurality of pages. An encoding unit that encodes the image data stored in the first memory, and a second memory that stores the image data of the immediately preceding page,
The encoding means performs encoding by referring to the image data of the immediately preceding page stored in the second memory.

Further, according to the present invention, in a decoding method for decoding a code obtained by coding image data of a plurality of pages, a decoding means for decoding the code and a first memory for storing the image data decoded by the decoding means. A re-encoding unit that encodes the image data stored in the first memory; and a second unit that stores the code encoded by the re-encoding unit.
Memory and re-decoding means for decoding the code stored in the second memory, and when the decoding means decodes the code that refers to the image data of the immediately preceding page, the re-decoding means decodes the code. The above-mentioned image data is referred to for decoding, and the re-encoding means performs encoding by referring to only the image data of the page to be encoded.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1> FIG. 1 is a block diagram showing the configuration of the device of the present invention. In the figure, reference numeral 1 denotes a computer, which includes hardware (not shown) such as a CPU, a memory, a hard disk, a floppy (registered trademark) disk drive, a keyboard, a mouse, a monitor, and a parallel port. Reference numeral 2 denotes an operating system, which manages the hardware of the computer 1, software such as applications 3, printer drivers 4, and port drivers 5. The application 3 is, for example, application software such as a word processor, and creates and prints a document according to an instruction from the operator.

A printer driver 4 receives a print command issued by the application 3 via the operating system 2 and converts the print command into a printer command interpretable by the printer 6. A port driver 5 receives the printer command converted by the printer driver 4 via the operating system 2 and sends it to the printer 6 via the parallel port. A printer 6 prints according to a printer command received from the port driver 5.

FIG. 2 is a block diagram showing the configuration of the printer 6.

In FIG. 2, reference numeral 11 is a parallel port, which receives a printer command from the computer 1.
A FIFO (first in first out) memory 12 stores the encoded data received by the parallel port 11, and outputs the stored data to the decoding circuit 13 in a first-in first-out order. The decoding circuit 13 decodes the code string data stored in the FIFO memory 12 and outputs it to the printer engine 14 and the re-encoding circuit 17. The printer engine 14 is a laser beam printer engine, and prints according to the image data output by the decoding circuit 13 according to an instruction from the control circuit 15.

Reference numeral 15 is a control circuit, for example, one chip C
It is composed of a PU and controls the parallel port 11, the FIFO memory 12, the decoding circuit 13, the re-encoding circuit 17, the page memory 18, the re-decoding circuit 19 and the printer engine 14. A re-encoding circuit 17 encodes the image data output from the decoding circuit 13 and outputs the encoded image data. A page memory 18 stores the code of at least one page output from the re-encoding circuit 17. A re-decoding circuit 19 decodes and outputs the code encoded by the re-encoding circuit 17 and stored in the page memory 18.

The printing operation will be described below.

When the operator operates the application 3 on the computer 1 side to generate print data and gives a print instruction to the print data, the print instruction is passed from the application 3 to the printer driver 4 via the operating system 2. The printer driver 4 converts the image data into image data based on the print command issued from the application 3. Then, the printer driver 3 generates coded data from the created image data based on a coding procedure described later,
It is output together with a print control command that specifies the paper size, the line length and the number of lines of bitmap data, a compression parameter specification command that specifies compression parameters, and a page break command that indicates the end of a page.

The port driver 5 is the printer driver 3
Sends a series of printer commands created by the printer 6 to the printer 6. The control circuit 15 receives the printer command via the parallel port 11. If the received printer command is a print control command or a compression parameter designation command, it is held in the control circuit 15 for print control. If the received printer command is encoded data, it is stored in the FIFO memory 12. afterwards,
When the completion of receiving the printer command forming one page is detected by receiving the page end command, the printer engine 14 is instructed to start printing. When the start of printing is instructed, the printer engine 14 requests the decoding circuit 13 to output image data when it becomes possible to accept the image data.

When the printer engine 14 is requested to output the image data, the decoding circuit 13 uses the FIFO.
The encoded data is read from the memory 12 and the decoded image data is output to the printer engine 14. In this way, the encoded data is sequentially decoded and output as image data, and when the output of the image data is completed, the printing of one page is completed.

The re-encoding circuit 17 encodes the output image data every time the decoding circuit 13 outputs the image data. The encoding process performed by the re-encoding circuit 17 may be any encoding process as long as the encoding process is performed by referring to only the data of the previous page without referring to the data of the previous page. , The data is encoded only by referring to the data on the upper side only, on both the left side and the upper side, or on the left side by a predetermined number of bytes and the position on a predetermined number of lines. The code encoded by the re-encoding circuit 17 is stored in the page memory 18.
When the printing of one page is completed in this way, the image data of the printed page is encoded and stored in the page memory 18.

Subsequently, when the reception of the printer command forming the second page is completed, printing is started in the same manner, and the image data is sequentially output to the printer engine 14 and encoded by the re-encoding circuit 17 to be page memory. 18 is stored. Further, the re-decoding circuit 19 starts the operation according to the instruction of the control circuit 15 before the printing of the second page is started, and encodes the image data of the immediately preceding page stored in the page memory 18. Read and decode the code. The area where the read code is stored becomes an empty area.

The re-decoding circuit 19 outputs the data decoded by the decoding circuit 13 in step with the output of the image data. This data is used as reference data when the decoding circuit 13 decodes a code that refers to the image data of the previous page, and is discarded without being used otherwise.

Next, the codes generated by the printer driver 4 shown in FIG. 2 will be described with reference to the tables shown in FIGS.

FIG. 3 is a diagram showing an example of codes generated by the printer driver 4 shown in FIG. The codes described in the present embodiment are: upper copy for copying a data string of a line on a predetermined line, left copy for copying a data string of a predetermined byte left of the same line, and before copying a data string at the same position on the previous page. One of four types of operations of page copy and raw data for directly specifying data is specified. The predetermined position referred to by the upper copy and the left copy has a value corresponding to the cycle of the dither matrix used for binarization.

As shown in FIG. 3, when the bit of the command code is "0", it is a RAW command, and the subsequent 8
Specify the bit data as it is as raw data.

When the bit of the command code is "10", the command is a COPY UP command, and the upper copy is performed by the number of bytes indicated by the subsequent count code.

The command code bit is "110".
In the case of, the command is a COPY LEFT command, and copying is performed by the number of bytes indicated by the subsequent count code.

The command code bit is "111".
If "0", COPY PREVIOUS PAGE
This is a command, and the previous page is copied by the number of bytes indicated by the subsequent count code.

The command code bit is "1111".
If it is "0", it is a COUNT HIGH command,
CO that is 64 times the number indicated by the subsequent count code
PYUP, COPY LEFT or COPY PRE
Indicates addition to the VIOUS PAGE command count.

Further, the bit of the command code is "1111".
In the case of "1", it is an EOB command and indicates the end of the code string.

FIG. 4 shows an example of a count code following the code shown in FIG.

As shown in the figure, when the bit of the count code is "111111", it is the COUNT0 code, which indicates that the count is zero.

When the bit of the count code is "0", it is the COUNT1 code, which means that the count is 1.

When the bit of the count code is "10", it is a COUNT2-3 code, and it indicates that the count is a value obtained by adding 2 to the subsequent 1 bit.

Further, the bit of the count code is "110".
In the case of, it is a COUNT4-7 code, and indicates that the count is a value obtained by adding 4 to the subsequent 2 bits.

The bit of the count code is "111".
In the case of "0", it is a COUNT8-15 code and indicates that the count is a value obtained by adding 8 to the following 3 bits.

The bit of the count code is "1111".
In the case of "0", it is a COUNT16-31 code, and indicates that the count is a value obtained by adding 16 to the following 4 bits.

The bit of the count code is "1111".
In the case of "10", it is a COUNT 32-63 code, and indicates that the count is a value obtained by adding 32 to the following 5 bits.

Next, with reference to FIG. 5, an example of reference numerals shown in FIGS. 3 and 4 will be described.

The code string "00000000 011001
01 01111101 00111011 1111
1111 10000000 "is interpreted as shown in FIG. First of all, the first "0" is a RAW command, so
The subsequent 8-bit data "00000000" is directly specified as raw data.

Next, "110" is a left copy command, and since the following "0" is a COUNT1 code, it indicates 1 byte left copy.

Next, "10" is an upper copy command,
Since the subsequent "10" is the COUNT2-3 code,
A value obtained by adding 2 to the subsequent 1 bit "1", that is, an upper copy of 3 bytes is shown.

Next, "11110" is COUNT HI.
It is a GH command, and the subsequent "10" is COUNT2.
Since it is a -3 code, it indicates that 64 times the value obtained by adding 2 to the subsequent 1 bit "0", that is, 128 is added to the count of the subsequent command.

Next, "1110" is the previous page copy command, and the subsequent "111111" is the COUNT0 code, and therefore indicates 0 byte previous page copy. However, in this case, since the COUNT HIGH 2 command precedes, 128 is added to indicate 128-byte previous page copy.

Next, "11111" is an EOB command and indicates the end of the code string. Continue to "000000
"0" is a padding for aligning to a byte boundary and has no special meaning.

Next, the details of the processing of the printer driver 4 will be described with reference to the flowchart shown in FIG.

When the printer driver 4 is called from the operating system 2, it is first determined in S1 whether the calling type is a drawing command. If the call type is a drawing command, the drawing process is performed in S2. Specifically, a character, a figure, a bitmap, or the like instructed by the application 3 via the operating system 2 is converted into an 8-bit grayscale image, recorded, and the process ends.

If the calling type is not a drawing command in S1, it is determined in S7 whether the calling type is a page end command. If the call type is the page end command, binarization processing is performed in S8. Specifically, the 8-bit grayscale image recorded in S2 is converted into a monochrome 1-bit image using a dither matrix.

Next, in S9, the print condition designation command,
Specifically, it outputs a command that specifies conditions necessary for printing, such as paper size, paper cassette, resolution, number of gradations, number of bytes per line, number of lines per page.

Next, in step S10, an upper copy vertical offset value for specifying the position of the copy source at the time of the upper copy used at the time of encoding, and the left side of the same line at the time of copying, the number of bytes left of the same line. Outputs a compression parameter specification command that specifies the left copy horizontal offset value that specifies whether or not the position is.

Here, the upper copy vertical offset value and the left copy horizontal offset value are used in advance by theoretically or experimentally obtaining optimum values according to the dither matrix used in S8. .

Next, in S11, the image data is encoded according to the encoding procedure described later. At this time, encoding is performed using the upper copy vertical offset value and the left copy horizontal offset value specified by the compression parameter specification command output in S10. Next, in S12, an image data command header designating the size and the number of lines of the image data encoded in S11 is output. Next, in S13, S1
The image data encoded in 1 is output. Next, S1
At 4, a page break command designating the end of the page is output. Next, in S15, the image data of the current page is transferred to the previous page memory, and the process ends.

If the call type is not the page end command in S7, other processes corresponding to the call type are performed in S16, for example, a process corresponding to a page start command or a printer capability inquiry command. ,finish.

Details of the encoding process of S11 of FIG. 6 will be described below with reference to FIG.

First, in S51, the line number Y is initialized to 0. Next, in S52, the byte offset X from the beginning of the line is initialized to 0. Next, in S53, it is determined whether the upper position is in a valid image area. In particular,
It is determined whether the number of lines indicating the upper copy position output in S47 of FIG. 6 is smaller than the line number Y. If the number of lines indicating the upper copy position is not smaller than the line number Y, it means that the upper position is in a valid image area. Therefore, in S54, the current position (X, Y) and the upper position (X, Y- The length at which the byte string starting from the number of lines indicating the upper copy position) continuously matches is calculated. At this time, if the lines match continuously up to the end of the line, the line is cut off.
If the length of consecutive matches exceeds 4095 bytes, which is the maximum value of the count code, the length is cut off at 4095 bytes.

Next, in S55, it is determined whether or not the length obtained in S54 is zero. If the length obtained in S54 is not 0, the length obtained in S54 is 63 in S56.
Determine if it is greater. The length obtained in S54 is 63
If it is larger, COUNT HIG at S57
The H command is output to the buffer, and then, in S58, the upper part of the count, that is, the quotient obtained by dividing the length obtained in S54 by 64 is encoded and output to the buffer, and the process proceeds to S59.
In S56, if the length obtained in S54 is not greater than 63, the process directly proceeds to S59.

Next, in S59, a COPY UP command is output to the buffer, and in S60, the lower part of the count, that is, the remainder obtained by dividing the length obtained in S54 by 64 is encoded and output to the buffer. To do.

If the number of lines indicating the upper copy position is smaller than the line number Y in S53 and the length is 0 in S55, the left position becomes the valid image area in S62. Determine if there is. Specifically, it is determined whether the number of bytes indicating the left copy position output in S47 of FIG. 6 is smaller than the byte offset X from the line head. If the number of bytes indicating the left copy position is not smaller than the byte offset X from the beginning of the line, it means that the left position is in the valid image area. Therefore, in S63, the current position (X, Y) is set.
And the length at which the byte string starting from the left position (X-the number of bytes indicating the left copy position, Y) is consecutively obtained. still,
At this time, if the lines match continuously up to the end of the line, the line is cut off at the end. If the length of consecutive matches exceeds 4095 bytes, which is the maximum value of the count code, the length is cut off at 4095 bytes.

Next, in S64, it is determined whether or not the length obtained in S63 is zero. If the length calculated in S63 is not 0, the length calculated in S63 is 63 in S65.
Determine if it is greater. The length obtained in S63 is 63
If it is larger, COUNT HIG at S66
The H command is output to the buffer, and then in S69, the upper part of the count, that is, the quotient obtained by dividing the length obtained in S63 by 64 is encoded and output to the buffer, and the process proceeds to S68. In S65, if the length obtained in S63 is not greater than 63, the process directly proceeds to S68.

Next, in S69, a COPY LEFT command is output to the buffer, and in S60, the lower part of the count, that is, the remainder obtained by dividing the length obtained in S63 by 64 is encoded and stored in the buffer. Output.

If the number of bytes indicating the left copy position is smaller than the byte offset X from the beginning of the line in S62 and the length is 0 in S64, S69.
At, it is determined whether a valid image is stored in the previous page memory. Specifically, it is determined whether the page number is 1. If the page number is not 1, it means that the image data has been transferred to the previous page memory in S15 of FIG. 6, so in S70 the current position (X, Y) of the image data of the current page and the previous page memory. The length at which the byte string starting from the current position (X, Y) of the image data stored in is consecutively obtained is obtained. , Shall be terminated at the end of the line. If the length of consecutive matches exceeds 4095 bytes, which is the maximum value of the count code, 4
It shall be terminated at 095 bytes.

Next, in S71, it is determined whether or not the length obtained in S70 is zero. If the length calculated in S70 is not 0, the length calculated in S70 is 63 in S72.
Determine if it is greater. The length obtained in S70 is 63
If it is larger, COUNT HIG at S73
The H command is output to the buffer, then in S74, the upper part of the count, that is, the quotient obtained by dividing the length obtained in S70 by 64 is encoded and output to the buffer, and the process proceeds to S75. In S72, if the length obtained in S70 is not greater than 63, the process directly proceeds to S75.

Next, in S75, COPY PREVI
Output OUS PAGE command to buffer, then S
At 60, the lower part of the count, that is, the remainder obtained by dividing the length obtained at S70 by 64 is encoded and output to the buffer.

If the page number is 1 in S69 and the length is 0 in S71, R is set in S76.
The AW command is output to the buffer, and then 1 byte of data at the current position (X, Y) is output to the buffer as raw data.

In any case, the process proceeds to S78 and the processed byte number is added to X. Next, in S79, it is determined whether X has reached the end of the line, that is, X is equal to the number of bytes in one line. If X is smaller than the number of bytes in one line, the process returns to S53 to continue the process. If X is equal to the number of bytes in one line, 1 is added to the line number Y in S80, and then it is determined in S81 whether the image processing is completed, that is, Y is equal to the number of lines in the image. .

If Y is less than the number of lines in the image,
The process returns to S52 and the process is continued. If Y is equal to the number of lines in the image, the EOB command is output to the buffer in S82, and then the bit "0" is output to the buffer in the number necessary for aligning to the byte boundary in S83, and the process is executed. finish.

Next, the details of the decoding circuit 13 shown in FIG. 2 will be described with reference to FIG. 9 is a block diagram showing details of the decoding circuit 13 shown in FIG.

In FIG. 9, the input buffer 21 has a FI
The code data read from the FO memory 12 is stored.
The input buffer 21 can store at least 4 bytes of data, the buffer becomes empty, and the FI
If there is data in the FO memory 12, the FIFO memory 1
Data is read from 2 and stored. Input buffer 21
When the number of processed bits held in the bit counter 23 becomes 8 or more, the unnecessary processed data is discarded.

The selector 22 is, for example, 11 sets of 8-input selectors, and the command decoding circuit 24 processes the code data stored in the input buffer 21 according to the number of processed bits indicated by the bit counter 23. The start position of the command is adjusted as necessary. This is necessary because the input buffer 21 holds data in byte units, whereas the command is variable length data in bit units and therefore has eight start positions.

The bit counter 23 has the input buffer 21.
The number of processed bits is stored in the code data stored in. The bit counter 23 also updates the value stored in the bit counter by adding the number of command bits output from the command decoding circuit 24. The bit counter 23 also subtracts the number of discarded bits when the input buffer discards processed data. The bit counter 23 also receives the EOB signal from the command decode circuit 23 when the command decode circuit 23 decodes the EOB command, and performs byte boundary alignment processing. Specifically, the lower 3 bits of the bit counter
If all the bits are 0, do nothing, otherwise add 8 and clear the lower 3 bits.

The command decoding circuit 24 is composed of, for example, a read-only memory or a wired logic, decodes the code data stored in the input buffer 21 and aligned by the selector 22, and counters according to the decoded command. 26, upper copy output circuit 2
7, previous page copy output circuit 28, left copy output circuit 29,
The raw data output circuit 30 and the bit counter 23 output various signals described above or below.

The counter 26 has COPY UP, COP
Y LEFT or COPY PREVIOUS PAG
The number of bytes processed by the E command is held, and is subtracted each time 1-byte data is output. Counter 26 is the top 6
The bit and the lower 6 bits can be set independently, and when the command decode circuit 23 decodes the COUNT HIGH command, the command decode circuit 23 outputs.
The added value of the number of processed bytes is stored in the higher order of the counter 26. In addition, the command decode circuit 23 has COPYUP, C
OPY LEFT or COPY PREVIOUS P
When the AGE command is decoded, the number of bytes processed by the command decoding circuit 23 is stored in the lower part of the counter 26.

The upper copy output circuit 27 reads the data at the upper copy position from the line buffer 31 according to the number of processing bytes held by the counter 26 and outputs it.

Line buffer 31 corresponding to the upper copy position
The address of is stored in a register incorporated in the upper copy output circuit 27. The initial value of this register is previously written with a value corresponding to the upper copy position by the control circuit 15, and is automatically added every time the decoding circuit 13 outputs 1-byte image data, and the result line When the end address of the buffer 31 is exceeded, the start address of the line buffer 31 is automatically reset.

The previous page copy output circuit 28 uses the counter 2
The image data at the same position on the previous page, which is output from the re-decoding circuit 19, is read and output according to the number of processing bytes held by 6.

The left copy output circuit 29 reads the data at the left copy position from the line buffer 31 and outputs it according to the number of bytes processed by the counter 26.

Line buffer 31 corresponding to the left copy position
The address of is stored in the register incorporated in the left copy output circuit 29. As the initial value of this register, a value corresponding to the left copy position is written in advance by the control circuit 15, and is automatically added every time the decoding circuit 13 outputs 1-byte image data, and as a result, When the end address of the line buffer 31 is exceeded, the start address of the line buffer 31 is automatically reset.

The raw data output circuit 30 outputs the 1-byte raw data output by the command decoding circuit 24.

The line buffer 31 holds the decoded data of a plurality of lines, and the upper copy circuit 27 or the left copy circuit 29.
The decoded data is read according to the address output by the upper copy circuit 27 and the previous page copy circuit 2
8. The decoded data output from the left copy circuit 29 or the raw data output circuit 30 is written at the current position.

The line buffer 31 corresponding to the current position
The address of is stored in a register built in the line buffer 31. The initial value of this register is written in advance with the start address of the line buffer 31 by the control circuit 15, and is automatically added every time the decoding circuit 13 outputs 1-byte image data. When the end address of the buffer 31 is exceeded, the start address of the line buffer 31 is automatically reset.

The command decode circuit 24 is a COPY U
When the P command is decoded, the subsequent count is decoded and stored under the counter 26, and a signal is output to the upper copy output circuit 27. The high order of the counter 26 is 0 when the COUNT HIGH command does not precede, and the COUNT HIGH when it precedes.
The high-order count indicated by the command is stored. The data at the upper copy position is read from the line buffer 31 and input to the upper copy output circuit 27. When the upper copy output circuit 27 outputs this data, the output decoded data is written at the current position of the line buffer 31. In this way, the decoded data is output until the counter 26 reaches 0.

The command decode circuit 24 uses the COPY P
When the REVIOUS PAGE command is decoded,
The subsequent count is decoded and stored in the lower part of the counter 26, and a signal is output to the previous page copy output circuit 28. Above the counter 26 is a COUNT HI
When the GH command does not precede, 0 is stored, and when it precedes, the upper count indicated by the COUNT HIGH command is stored. The data at the same position on the previous page is input from the re-decoding circuit 19 to the previous page copy output circuit 28. When the previous page copy output circuit 28 outputs this data, the output decoded data is written in the current position of the line buffer 31. In this way, the decoded data is output until the counter 26 reaches 0.

The command decoding circuit 24 uses COPY L
When the EFT command is decoded, the subsequent count is decoded and stored under the counter 26, and
A signal is output to the left copy output circuit 29. The high order of the counter 26 is 0 when the COUNT HIGH command does not precede, and the COUNT HI when it precedes.
The upper count indicated by the GH command is stored. The data at the left copy position is read from the line buffer 31 and input to the left copy output circuit 29. When the left copy output circuit 29 outputs this data, the output decoded data is written in the current position of the line buffer 31.
In this way, the decoded data is output until the counter 26 reaches 0.

When the command decoding circuit 24 decodes the RAW command, it outputs the subsequent 1-byte raw data to the raw data output circuit 30. Raw data output circuit 30
When this data is output by, the output decoded data is
It is written in the current position of the line buffer 31.

The command decode circuit 24 is COUNT
When the HIGH command is decoded, the subsequent count is decoded and stored in the upper part of the counter 26.

<Other Embodiments> In the above embodiment, encoding and decoding are performed in units of 1 byte of image data, but instead of this, other units such as 1 are used.
A pixel or 2 bytes may be used as a unit.

Further, in the above-mentioned embodiment, the black and white image is handled, but instead of this, a color image may be handled.

Further, in the above-mentioned embodiment, one pixel is composed of 1 bit, but it may be replaced by another value such as 2 bits, 4 bits or 8 bits.

Further, in the above embodiment, the decoding is performed by hardware, but instead of this, decoding may be performed by software. Also, in the embodiment described above,
Although the dither processing is performed, the dither processing may not be performed instead.

[0089]

As described in detail above, according to the present invention, since the coding is performed by referring to the same position on the previous page in addition to the left side and the upper side of the target position, the left and upper reference positions are referred to. Even if the image has a low correlation with, it can be efficiently compressed when encoding an image having a high correlation with the previous page, such as when the same background pattern is used in consecutive pages.

Further, in the present invention, since the image data of the previous page to be referred to is encoded and held, the image data of the previous page is held in a memory having a smaller capacity than in the case where the image data is held as it is. can do.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a system of the present invention.

FIG. 2 is a block diagram showing details of the configuration of a printer according to the present invention.

FIG. 3 is a table showing codes of the method of the present invention.

FIG. 4 is a table showing codes of the method of the present invention.

FIG. 5 is a diagram for explaining an actual example of codes according to the method of the present invention.

FIG. 6 is a flowchart showing a processing procedure of a printer driver according to the present invention.

FIG. 7 is a flowchart showing an encoding procedure of the method of the present invention.

FIG. 8 is a diagram showing an example of a background pattern.

FIG. 9 is a block diagram showing details of a decoding circuit according to the present invention.

[Explanation of symbols]

1 computer 2 operating system 3 applications 4 Printer driver 5 port driver 6 printer 11 parallel port 12 FIFO memory 13 Decoding circuit 14 Printer engine 15 Control circuit 17 Re-encoding circuit 18 page memory

Claims (2)

[Claims] 1. An encoding method for encoding image data of a plurality of pages, comprising: a first memory for storing image data of a page to be encoded; and image data stored in the first memory. And a second memory for storing the image data of the immediately preceding page,
The encoding method, wherein the encoding means encodes with reference to the image data of the previous page stored in the second memory. 2. A decoding method for decoding a code obtained by coding image data of a plurality of pages, the decoding means decoding the code, and a first memory storing the image data decoded by the decoding means. Re-encoding means for encoding the image data stored in the first memory, a second memory for storing the code encoded by the re-encoding means,
Re-decoding means for decoding the code stored in the second memory, wherein the decoding means decodes the image data decoded by the re-decoding means when decoding the code referring to the image data of the immediately preceding page. The decoding method is characterized in that the re-encoding means performs encoding by referring to only the image data of the page to be encoded while referring to the decoding.