JP2965084B2 - Image data compression method - Google Patents

Description

The present invention relates to a simple image data compression / expansion method for effectively compressing image data such as an image on a transfer side and decompressing data on a transfer side. About.

(Prior art) Conventionally, this type of image data compression / expansion method is based on the MH coding method and MR coding method used in G3 facsimile and the like, and the MMR coding method used in G4 facsimile and the like. By encoding the binary image data, the image data is compressed and the data transfer time is shortened.

These methods are based on CCITT Recommendations T.4 and T.6. Here, an outline of a conventional image data compression / decompression method will be described using an MH encoding method as an example.
Note that the MH encoding method encodes image data with a continuous length (hereinafter, referred to as a run length) of the same color pixels of white pixels and black pixels for each scanning line.

First, compression of image data will be described with reference to FIGS. FIG. 2 is an explanatory diagram showing an example of image data compression by the MH coding method, FIGS. 3 (a) and 3 (b) are diagrams showing the relationship between run length and makeup code, and FIG. 4 (a). , (B) shows the relationship between run length and terminating code.

The run length encoded by the MH encoding method is called a data code. In the MH encoding method, an EOL (End of Line) code before the data code is added and, if necessary, after the data code. A fill bit is added. Here, the format of the EOL code is “000000000001” _B. The fill bit is inserted immediately after the data code so that the sum of the EOL code, the data code, and the fill bit is equal to or greater than the defined minimum number of code bits for one scan line. Can not.). The format of the fill bit is a variable length “0” _B column.

For example, when 112 consecutive white pixels are compressed by the MH coding method, an EOL code (a in FIG. 2) is first added as shown in FIG. 2, and then a data code (b in FIG. 2) is obtained. Thereafter, a fill bit (the point c in the figure) is added.
Here, the data code at the point b in FIG.
A makeup code “11011” _B (refer to d in FIG. 3A) representing two consecutive white pixels and a terminating code “0000101” representing 48 consecutive white pixels represent two consecutive white pixels.
It is obtained by converting to 1 " _B (see the point e in FIG. 4 (b)).

In this way, the run length is encoded. Therefore, since the data transfer is performed in a compressed form of the image data, the transfer time is shorter than that before encoding.
Extremely short.

Similarly, when expanding the image data, the number of continuous pixels can be obtained by detecting the EOL code and analyzing the data code, and can be converted into the original image data.

As described above, the image data compression / expansion method of the prior art has been described by taking the MH encoding method as an example. However, these compression / expansion processes are performed by hardware (circuits) rather than by software (programs). However, since the processing speed is high, a dedicated LSI is generally used.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional image data compression / expansion method, since a dedicated LSI is used, it is necessary to determine whether or not to use the LSI from the beginning of the device design. Therefore, even if a dedicated LSI is not used, if it is judged that the processing capacity in the specifications can be satisfied and the design is advanced, the processing capacity in the specifications will be satisfied in the stage of evaluation by the actual machine later. When a problem such as being impossible, that is, taking too much time for data transfer occurs, as a countermeasure, it is necessary to take large-scale measures such as circuit change (addition) or to abandon improvement of processing speed. is there.

In particular, in an image reading apparatus that transfers image data to a connected device via a serial interface instead of a parallel interface, the image data transfer time is a factor that determines the processing capability of the system. The issue of competence is important.

Therefore, an object of the present invention is to solve the problem of the conventional processing capacity without using a dedicated LSI for data compression and decompression as in the past, and furthermore, on the data transfer side, arbitrarily continuous large amounts of the same data. A simple image that can easily perform data compression with a high compression ratio, and can easily perform data decompression for data restoration on the data transfer side, greatly reducing the data transfer time. An object of the present invention is to provide a data compression / decompression method.

(Means for Solving the Problems) According to a method for compressing image data of the present invention, in the method for compressing image data represented by “1” and “0” bit data, “0” bit data is equal to or more than a predetermined amount. In the case of continuous data, a plurality of index data indicating that the data is "0" are successively placed at the top, and then the length data indicating the data length of the data is continuously continued by the same number as the index data, whereby the position is determined. Bit data of “0” that is continuous for a certain amount or more is compressed.

(Operation) The image data reading device on the transfer side compresses “0” bit data in the image memory for storing the image data in the unit of bytes in the form of “index + length” when the data is continuous. When the bit data of “0” continues for a predetermined amount or more, a plurality of index data are successively placed at the head, and then the length data is continued for the same number of times as the index data. "
The image data is transferred to another connected device by compressing the bit data. In the connected device on the transferee side,
The number of bytes constituting the length is determined based on the number of indices in the received image data, and data decompression for data restoration is performed.

Therefore, in the present invention, the data transfer side can perform data compression at a high compression ratio on any continuous large amount of the same data without using a dedicated LSI as in the related art, and Data decompression for data restoration can be easily performed. Since the data compression can be performed at a high compression rate on the transfer side, the data transfer time from the image data reading device to another connection device is greatly reduced, and the problem of the processing capability unlike the conventional case does not occur.

(Example) Next, the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory diagram showing one embodiment of a data compression method according to the present invention.

FIG. 2A shows image data (binary display) before compression. This image data includes 60 continuous white pixels, which are divided into bytes in the image memory.
When expressed in hexadecimal, it becomes as shown in FIG.

In FIG. 6B, 60 consecutive white pixels are 2 bytes in byte units.
It becomes bit +7 byte + 2 bits, of which 7 byte is hexadecimal 00 _H, to do this the object of compression.

Form of compression, and FIG. (C) is an indicator (EOL codes referred to in the coding scheme) as shown in 00 _H 1 byte, 00 _H number of consecutive bytes (hereinafter, referred to as length.), Where It converted into 1-byte total of 2 bytes 07 _H indicating the 7 bytes.
This is the basic form of compression. The data that has been compressed as shown in FIG. In FIG. (C), indicators, and 00 _H fixed, other values (in bytes) considers the image data without compression, 00 _H
By defining that the byte following "" is always a length, the decompression side can identify whether the data is compressed data.

Therefore, even if the image data 00 _H pattern is 1 byte, it adds length 01 _H always after 00 _H. In this case, 00 _{for H} 1 byte would be represented by 2-byte 00 _H · 01 _H, rather than compression, becomes the extra increase the number of transfer data, but if not strictly between devices of the above definition However, the compression / decompression method of the main image data does not work.

Then, if the length exceeds (FF _H in hexadecimal) 255 bytes, if you do not want to complicate the process of compression and decompression image data, 255 bytes may be carried out in the aforementioned basic form (FIG. 5 (c )reference). However, in order to further increase the data compression ratio, the following extended compression method can be considered.

Aforementioned, the basic form of the compression index, although a one byte arrangement length, which 2-byte configuration, that is, when the index is 2 bytes (00 _H · 00 _H), length also 2 bytes (2 bytes Configuration The maximum length that can be represented by is hexadecimal FF
FF _H , 65535 bytes in decimal). The reason why the index is set to 2 bytes is that the compression format having the minimum byte configuration according to the length can be used by defining the continuous number of indexes = the byte configuration of the following length. Also, what should be noted about the extended compression format in which the index is 2 bytes is that the length immediately after the index is the most significant digit. Because it is, if temporarily when the length immediately after the indication to the least significant digit, the least significant digit is also for the same data, i.e. 00 _H as an index, whether an indicator for the extension, the length of the lowest This is to prevent a problem that the decompression side cannot determine whether the digit is a digit.

If the length immediately after the indicator is the most significant digit, the extension condition is that the length exceeds FF _H , so the extended length is 0100 _H , and the most significant digit is always a value greater than 00 _H Therefore, the above problem is eliminated. Incidentally, this mentioned in the present compression method "for compression is 00 _H only"
If the continuation of black pixels (usually FF _H ) is to be performed together with the compression of white pixels, an index other than 00 _H must be used to distinguish it from white pixel compression. , even if the length immediately after the index the most significant digit at the time of the other than the 00 _H, there is a risk of the index and the same data. For this reason, the above-mentioned "is the subject of compression 00 _H only"
Condition must be absolute.

The above-described extended compression will be described with reference to a specific example in FIG. FIG. 5 is an explanatory view showing another embodiment of the image data compression method according to the present invention.

If there are 10200 consecutive white pixels as image data as shown in FIG. 5 (a), it is represented in hexadecimal notation (b).
It becomes as shown in. Furthermore, if the structure of the length is assumed to be the basic form (2 bytes each for 1 byte for both the index and the length), as shown in FIG. 10 (c), 10200 pixels are 1275 bytes, and the shape is formed in units of 255 bytes. 5 sets (5 × 2
= 10 bytes).

However, if further compression in expanded form, 10200 pixels at 1275 bytes, since 1275 bytes is hexadecimal 4fb _H, it may be the length configuration 2 bytes. Therefore, in the case of the extended type as shown in FIG. 10D, the structure of the index and the length is only 2 bytes each, that is, a total of 4 bytes. Can be done. Incidentally, the (d) of FIG sequence of length as shown in the a person upper address closer to the index, there is no such the most significant address is 00 _H.

Next, an application example of the image data compression / expansion method of the present invention will be described with reference to FIGS. 6 and 7. FIG. FIG. 6 is a diagram showing a configuration example of the image reading system, and FIG. 7 is a detailed explanatory diagram showing a flow of image data in FIG.

First, the image reading system will be described with reference to FIG. In FIG. 1, reference numeral 11 denotes an image reading device, and the image reading device 11 includes a compression conversion unit. Reference numeral 12 denotes a higher-level device connected to the image reading device 11 via a serial interface 13, and the higher-level device 12 includes a decompression conversion unit. Further, a printer 14 or the like for outputting image data is generally connected to the host device 12, if necessary.

Next, the internal configuration of each device in FIG. 6 will be described with reference to FIG. 7, focusing on the flow of image data.

First, in the image reading device 11, the image data read by the image reading sensor 11-1 is temporarily stored in the image memory 11-2. Normally, only hardware transfers data between the image reading device 11 and the image memory 11-2. Next, the image reading device
A built-in main control unit (not shown) operates the compression conversion unit 11-3. The compression conversion means 11-3 is provided in the image memory 11
The image data stored in -2 is taken out one byte at a time, compressed, and stored in the transmission buffer 11-4. The transmission buffer 11-4 stores compressed image data having a small capacity, which is transferred to the higher-level device 12 by the serial interface 13. At the same time as this transfer
The same operation is performed in the image reading device 11. That is, the image data read by the image reading sensor 11-1 is stored in the image memory 11-2, and the image data is further taken out one byte at a time from the image memory 11-2, and compressed and converted by the compression conversion means 11-3.
And is stored in the transmission buffer 11-4. Then, the serial interface 13 is transmitted from the transmission buffer 11-4.
Is transferred to the upper-level device 12 via the.

Next, in the host device 12, the image data received via the serial interface 13 is temporarily stored in the reception buffer 12-1. Next, a main control unit (not shown) built in the host device 12 operates the decompression conversion unit 12-2. The decompression conversion means 12-2 extracts the image data one byte at a time from the reception buffer 12-1, performs decompression processing, returns the image data before compression, and stores it in the editing memory 11-3. From the editing memory 11-3, the image data is transferred to the printer 14 as necessary.
Output to

As described above, the image data is transferred from the image reading device 11 to the higher-level device 12 (further, the printer 14) as the connection device.

Next, specific processing by the compression conversion means 11-3 and the expansion conversion means 12-2 to which the present invention is applied will be described.

First, the image data compression conversion processing by the compression conversion means 11-3 will be described with reference to FIG. FIG. 8 is a flowchart of a compression conversion process by the image data compression method according to the present invention. FIG. 8 shows an example of a length counter for easy understanding of the processing flow.

The compression conversion means 11-3 firstly stores the image memory 11-2.
Extract image data (byte) from the data (step in FIG. 8)
S1). Then (usually white consecutive pixels.) The retrieved image is 00 _H it is determined whether or not (step S2 in FIG.), 00
If it is not _H , the image data is out of the compression target, and the extracted image data is stored as it is in the transmission buffer 11-4 (step S3 in FIG. 3). Also, if there in the extracted image data is 00 _H, because it is the compression of the target, the parameter I (pointer representing the length counter to slide into updated) required compression, J (the number of length counter used: LNG (0) to LNG (n-1) (Length counter that actually counts the number of consecutive bytes. Counters 0 to n: n are the maximum number defined by the length counter system.) And the counter number is n-1
Becomes ) Are all initially set to “0” (step S4 in the figure).

Then, since the extraction already 1 byte 00 _H, the length counter +1 (byte) (in the drawing step
S5).

Next, in order to start counting the number of consecutive bytes, first, the next image data is fetched from the image memory 12-2 (step S6 in FIG. 6).

Taken out image data is 00 _H unless, (at this time, use J to know whether it has counted up to any length counter.) Minute length which counts up to the end of the counting length of the transmission buffer 11-4 Then, the process returns to step S1 again (steps S7 and S8 in the figure).
If also retrieved image data is 00 _H, a length counter indicating pointer I of the length counter to be updated to +1 (byte) (step S7, S9 in drawing).

Next, it is determined whether or not the lens counter that has just counted up has overflowed (digit overflow: FF _H → 00 _H ) (step S10 in the figure), and if it has not overflowed, the pointer I of the length counter to be updated is updated. Return to "0" to indicate the length of the lower byte (step S1 in FIG.
1), return to the next screen data retrieval (Step S in the same figure)
6).

If the length counter has overflowed, the pointer I of the length counter to be updated is updated (+1 is added so as to indicate the length counter of the next upper digit) (step S12 in the figure), and the length to be further updated The length counter indicated by the pointer I of the counter is incremented by +1.
(Byte) (step S13 in the figure).

Since an overflow has occurred in the length counter, an index (00 _H ) for extended compression is stored in the transmission buffer 11-4 (step S14 in the figure), J is updated (step S15 in the figure), and again An overflow is determined (step S16 in the figure).

In this manner, the data compression including the extended compression is performed, and the compressed image data is prepared in the transmission buffer 11-4, and transferred to the host device 12 as a connection device at a certain timing. To go.

Next, the expansion conversion processing of the received image data by the expansion converter 12-2 will be described with reference to FIG. still,
FIG. 9 is a flowchart of a decompression conversion process by the image data decompression method according to the present invention. FIG. 9 shows an example of a length counter for easy understanding of the processing flow.

The decompression / conversion means 12-2 extracts the image data (1 byte) first received by the serial interface 13 from the reception buffer 12-1 (step S21 in FIG. 9).

Next, the fetched image data is 00 _H it is determined whether or not (step S22 in FIG.), 00 because it is covered by the _H unless extended, storing image data taken out as the editing memory 12-3 (Step S23 in the figure). Also, if there in the extracted image data is 00 _H, because it is the extension of the object, for knowing the parameters I (or length many bytes configuration required decompression processing, and for storing the received length to the length counter Pointer) is set to "0" (step S24 in the figure).

Next, the index 00 is taken out from the receive buffer 12-1 the data of the next byte following the _H (step S25 in FIG.), The data is 00 _H (continuous indication) or not (in the drawing step S2
6). If there in the extracted data is 00 _H, parameter I is updated (count of bytes constituting Length) (figure in step S27), reception of the next data buffer 12-1
(Step S25 in the figure). Step S26
In, unless the data is 00 _H was taken out from the receiving buffer 12-1, since the length of the most significant digit, the length counter indicating the data parameter I is, step S28 in (FIG storing for temporary storage ).

Next, the number of indexes (= I) counted so far is
Until it becomes "0" (the number of indices = the number of bytes constituting the length, all of the received data may be regarded as length). Data is sequentially taken out from the reception buffer 12-1 (steps in the figure). S30), the parameter I is decremented by 1 (step S31 in the figure), and the length is stored in the length counter (step S28 in the figure).

Thus, the parameter When I becomes "0", because extraction of the length is completed, then temporarily stored reads the length from the length counter had, length worth of 00 _H
The data is stored in the editing memory 12-3 (step S3 in FIG.
2) Return to step S21.

In this way, data expansion including expansion is performed, and the original read image data is restored in the edit memory 12-3.

In the above embodiment, the compression conversion means 11-3 is
The image reading apparatus 11 includes a main control unit and a storage device (hard disk) storing a compression conversion program. The main control unit performs a compression conversion process according to the compression conversion program. -3 may be realized by microprogramming or simple hardware.

Further, in the above embodiment, the expansion conversion means 12-2
The main control unit includes a main control unit and a storage device (hard disk) storing a decompression conversion program. The main control unit performs decompression conversion operation according to the decompression conversion program. 12-2 may be configured by a microprogram or simple hardware.

As can be seen from the above description, according to the present invention, on the data transfer side (image reading device 11), data compression can be performed at a high compression ratio on arbitrary continuous large amounts of identical data, and Data decompression for data restoration can be easily performed on the data transfer side (upper device 12). Data compression at the data transfer side (image reading device 11) can be performed at a high compression ratio, greatly reducing the time required for data transfer from the image reading device to the higher-level device 12, which is another connected device, and processing capacity as in the past. No problem arises.

The present invention is not limited to the present embodiment, and various applications and modifications can be considered without departing from the gist of the present invention.

(Effects of the Invention) As described above, according to the present invention, any continuous large amount of the same data can be obtained on the data transfer side by a simple method without using a dedicated LSI for data compression and decompression as in the related art. In this case, the data can be compressed and transferred at a high compression ratio, and the data transfer side can easily perform the data decompression to restore the original data. Therefore, according to the present invention, image data is compressed and transferred at a high compression rate, so that the transfer time can be greatly reduced, whereby the image data can be transferred to a connection device (such as a host device) by an interface (particularly, a serial interface). In the image data reading apparatus which transfers the image data via the image processing apparatus, it is possible to easily prevent a decrease in the processing capacity of the system due to the transfer time, and to prevent the problem of the processing capacity from occurring in the related art. Can be.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of an image data compressing method according to the present invention, FIG. 2 is an explanatory view showing a conventional image data compressing method using the MH coding method, and FIG. 3 is a run-length and make-up method. FIG. 4 is a diagram showing a relationship between an up code, FIG. 4 is a diagram showing a relationship between a run length and a terminating code,
FIG. 5 is an explanatory diagram showing another embodiment of the image data compression method according to the present invention, FIG. 6 is a simplified diagram showing an example of the configuration of an image reading system, and FIG. 7 shows the flow of image data in FIG. FIG. 8 is a flowchart showing one embodiment of the image data compression method according to the present invention, and FIG. 9 is a flowchart showing one embodiment of the image data decompression method according to the present invention. 11 image reading device 11-1 image reading sensor 11-2 image memory 11-4 transmission buffer 12 host device 12-1 reception buffer 12-3 ... Edit memory, 13 ... Serial interface, 14 ... Printer.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kenichi Nishikawa 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (56) References JP-A-62-58780 (JP, A) (58) ) Surveyed field (Int.Cl. ⁶ , DB name) H04N 1/41-1/419

Claims (1)

(57) [Claims] 1. A method of compressing image data represented by bit data of "1" and "0", wherein when bit data of "0" continues for a predetermined amount or more, it is determined that the data is "0". A plurality of index data indicated at the beginning are successively placed at the head, and then the length data indicating the data length of the data is continued continuously for the same number as the index data, thereby compressing the bit data of “0” which is continuous for the predetermined amount or more. A method for compressing image data, characterized in that: