JP3531844B2 - Image processing device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing device for encoding pixel data into compressed data, an image processing device for decoding compressed data into density data, and an image processing device for encoding pixel data into compressed data and then decoding into density data. And an image processing device that does.

[0002]

2. Description of the Related Art Currently, image processing apparatuses include a scanner apparatus for inputting image data, a printer apparatus for outputting image data, and a digital copying machine for inputting and outputting image data.

Such a digital copying machine will be described below with reference to FIG. 16 as a first conventional example of an image processing apparatus. 16 is a block diagram showing the digital copying machine 1 which is an image processing apparatus.

First, the digital copying machine 1 includes a scanner section 2
And an A / DC (Analog / Digital Convertor) 3, an image processing section 4, and a printer section 5. The scanner unit 2
Reads image data from a document (not shown), and the A / DC 3 converts analog image data into digital. The image processing unit 4 performs image processing such as gamma conversion and image quality correction on the image data, and the printer unit 5
Print out on an image data print sheet (not shown).

Such a digital copying machine 1 generally stores the captured image data in a memory so that the image data can be repeatedly used and the image data can be processed such as rotation and inversion. It is possible.
However, since the image data has a huge amount of data, if this is simply stored in the memory, a large capacity memory is required.

Particularly, the recent digital copying machine 1 is designed to perform high-quality image processing by treating each of the pixel data in the image data as a multi-gradation, but it forms the image data. Each of a large number of pixel data,
If simply converted to multi-tone density data, the amount of data becomes enormous and an extremely large capacity memory is required.

For this reason, encoding of image data into compressed data to reduce the amount of data and decoding of compressed data into image data have been carried out. Such encoding and decoding will be described below with reference to FIGS. 17 and 18. Note that FIG. 17 is an explanatory diagram showing encoding of image data, and FIG. 18 is a schematic diagram showing an algorithm for realizing the encoding.

First, when image data is encoded into compressed data according to a predetermined algorithm as shown in FIG. 18, as shown in FIG. 17, multi-gradation pixel data forming the image data is converted into "4 × 4". The block data is generated by dividing it into blocks, and the density data Lij (16 bytes) is calculated by the number of black and white of this block data. The average data La and the gradation width index Ld are calculated from the maximum value Lmax and the minimum value Lmin of the density data Lij, and the quantization thresholds P1 and P2 are calculated from the average data La and the gradation width index Ld. With the thresholds P1 and P2, the code φij (16 × 2 bits = 4 bytes) for each pixel data is calculated as the average data La (1
Byte) and gradation width index Ld (1 byte) to assign density data Lij (16 bytes) to compressed data (4 bytes).
+ 1 + 1 = 6 bytes).

By such encoding, the 16-byte density data becomes 6-byte compressed data, so that the data amount can be set to "3/8".

When decoding the compressed data into image data, the quantized representative values Q1 to Q4 are calculated from the average data La of the compressed data and the gradation width index Ld, and the quantized representative values Q1 to Q4 are calculated. Decode the compressed data into block data by assigning it to the code φij for each pixel data,
Image data is reproduced by arranging pixel data corresponding to the density data.

Note that Pi of the above-mentioned algorithm is a quantization threshold value at the time of encoding, and Qj is a quantization representative value at the time of decoding. This quantization threshold Pi and the quantization representative value Qj
Is calculated as P1 = La + 1 / 2Ld P2 = La-1 / 2Ld Q1 = La + 3 / 4Ld Q2 = La + 1 / 4Ld Q3 = La-1 / 4Ld Q4 = La-3 / 4Ld as in the algorithm of FIG. .

When the pixel data is encoded into the compressed data as described above, a large amount of image data can be compressed into a small amount, so that it can be stored in the memory and used for editing processing and the like. Therefore, a digital copying machine 6 that realizes such a thing will be described below as a second conventional example of an image processing apparatus with reference to FIGS. 19 and 20.

Regarding the digital copying machine 6, the same parts as those of the digital copying machine 1 described as the first conventional example are designated by the same names and reference numerals, and detailed description thereof will be omitted. FIG. 19 is a block diagram showing the whole of the digital copying machine 6, and FIG. 20 is a block diagram showing essential parts.

First, in this digital copying machine 6, FIG.
As shown in FIG. 5, the encoding / decoding unit 7 is connected to the image processing unit 4, and the printer unit 5 is connected to the changeover switch 8 for selecting one of the encoding / decoding unit 7 and the image processing unit 4. There is. A first image storage unit 9 is connected to the encoding / decoding unit 7, and a second image storage unit 10 is connected to the first image storage unit 9.

Next, the structure of the encoding / decoding unit 7 is shown in FIG.
It will be described below based on 0. First, the image processing unit 4
In addition, a 4-line FIFO (First In
First Out) 11 and the encoding unit 12 are sequentially connected, and the encoding unit 12 is connected to the first image storage unit 9. The first image storage unit 9 includes decoding units 13 and 4
The line FIFOs 14 are sequentially connected, and the 4-line FIFOs 14 are connected to the changeover switch 8.

As will be described later in detail, the four lines F
The IFO 11 converts pixel data into block data,
The encoding unit 12 functions as a density calculating unit and a data calculating unit, and generates compressed data from block data. The decoding unit 13 decodes the compressed data into block data, and the 4-line FIFO 14 generates image data from the block data.

The first image storage section 9 is a RAM (Random
Access memory) and the like, which temporarily stores compressed data at high speed, but has a small storage capacity. The second image storage unit 9 is composed of an HDD (Hard Disk Drive) or the like and stores a large amount of compressed data, but its storage speed is low.

In the digital copying machine 6 having such a configuration, the image data read from the document by the scanner unit 2 is encoded into the compressed data by the encoding / decoding unit 7, and the compressed data is stored by the first image storage unit 9. It can be temporarily stored and then stored in the second image storage unit 10. further,
It is also possible to sequentially read the compressed data accumulated in the second image storage unit 10 via the first image storage unit 9, decode the image data by the encoding / decoding unit 7, and reproduce it on the printing paper by the printer unit 5.

The image data read from the original by the scanner unit 2 can be directly copied on the printing paper by the printer unit 5. In the case of directly copying the image data as described above, the image processing section 4 is connected to the printer section 5 by the changeover switch 8 and the copying operation is executed similarly to the digital copying machine 1 described above as the first conventional example. To be done.

When the image data is encoded and then decoded, the changeover switch 8 connects the encoding / decoding unit 7 to the printer unit 5. In this case, the encoding / decoding unit 7
Then, the 4-line FIFO 11 accumulates four lines of line data that the image processing unit 4 actually outputs for one pixel data, thereby dividing the multi-tone pixel data into blocks of “4 × 4”. Generate block data. The encoding unit 12 calculates the density data Lij by counting the number of black and white for each of the block data output from the 4-line FIFO 11 and calculates the density data Lij.
ij is encoded into compressed data by a predetermined algorithm.

More specifically, the maximum value L of the density data Lij
Since the average data La and the gradation width index Ld are calculated from the max and the minimum value Lmin as La = (Lmax + Lmin) / 2 Ld = (Lmax-Lmin) / 2, this is assigned to the code φij for each pixel data. By setting, compressed data obtained by encoding pixel data is generated.

Therefore, the compressed data in which the pixel data is encoded by the encoding / decoding unit 7 in this way is accumulated in the second image storage unit 10 via the first image storage unit 9. When decoding the compressed data thus accumulated into pixel data, the compressed data is sequentially read from the second image storage unit 10 through the first image storage unit 9, and this compressed data is encoded and decoded. Decoded by 7 into pixel data.

More specifically, the decoding unit 1 of the encoding / decoding unit 7
3 is the average data La of the compressed data and the gradation width index Ld.
Then, the quantized representative values Q1 to Q4 are calculated as Q1 = La + 3 / 4Ld Q2 = La + 1 / 4Ld Q3 = La-1 / 4Ld Q4 = La-3 / 4Ld, and pixels are quantized to these quantized representative values Q1 to Q4. By setting the code φij for each data, the compressed data is decoded into block data. The block data composed of this “4 × 4” pixel data is stored in the 4-line FIFO 14 and then output to the printer unit 5 as 4-line image data. Therefore, the printer unit 5 prints the image data on a print sheet. Print out.

As described above, the image data read from the original by the scanner unit 2 can be encoded and stored as compressed data, and this compressed data can be decoded into image data and reproduced by the printer unit 5 on printing paper. . Moreover, since the compressed data can be stored in the image storage units 9 and 10, the editing process of the compressed data can be repeatedly executed. At this time, the image storage units 9 and 10 only need to store the compressed data obtained by encoding the image data, so the storage capacity thereof is reduced. Further, since the second image storage unit 10 having a large storage capacity is connected to the first image storage unit 9 having a high storage speed, a small amount of compressed data can be stored at a high speed, and a large amount of compressed data can be stored. It can be stored for a long time.

[0025]

The digital copying machine 6 described above compresses the data capacity by encoding image data into compressed data, but further data compression is desired. Particularly, in the above-mentioned digital copying machine 6, since the second image storage unit 10 having a large storage capacity but a low storage speed is used, the data capacity is further compressed in order to prevent delay in data transfer. There is a need.

[0026]

The invention according to claim 1 is
Provided is a data decomposing means for generating a large number of block data by dividing a large number of pixel data forming multi-tone image data into blocks, and calculating density data of each of the plurality of pixel data forming the block data. A density calculation means is provided, and data calculation means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data for each block data is provided, and the difference calculation for calculating the difference between the gradation width index between the previous time and this time is calculated. Means is provided, and a data comparison means is provided for determining whether or not the difference of the gradation width index is within a preset allowable range.If the difference is not within the allowable range, an identifier indicating the adoption of the gradation width index at this time is provided. A first encoding unit is provided which is inserted at the bottom of the average data and generates compressed data by the average data, the gradation width index, and the code for each pixel data. If there, insert the identifier indicating the adoption of the previous tone width index to the lowest average data, by a code for each average data and pixel data, provided the second encoding means for generating compressed data.

The invention according to claim 2 is provided with an identifier judging means for judging the presence or absence of the gradation width index by reading the identifier from the lowest order of the average data of the compressed data. Provided is a first decoding means for generating density data, and a second decoding means for generating density data from the current average data, the previous gradation width index, and the code for each pixel data this time when there is no gradation width index. It was

According to a third aspect of the present invention, the block data is formed by providing a data decomposing means for dividing a large number of pixel data forming a multi-gradation image data into a predetermined number of blocks to generate a large number of block data. A density calculating means for calculating each density data of a plurality of pixel data is provided, and a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data is provided for each block data,
The difference calculation means for calculating the difference between the gradation width indexes of the previous time and this time is provided, and the data comparison means for determining whether or not the difference of the gradation width indexes is within a preset allowable range is provided. If there is not, an identifier indicating the adoption of the gradation width index this time is inserted at the bottom of the average data, and the first encoding means for generating compressed data by the average data, the gradation width index, and the code for each pixel data. If the difference is within the allowable range, an identifier indicating the adoption of the previous gradation width index is inserted at the bottom of the average data, and compressed data is generated by the average data and the code for each pixel data. (2) An encoding means is provided, and an identifier determining means is provided to read the identifier from the lowest of the average data of the compressed data and determine the presence or absence of the gradation width index. A first decoding means for generating provided, when tone width index is not provided with the second decoding means for generating density data from the current average data and the previous tone width index and sign of each current pixel data.

According to a fourth aspect of the present invention, the block data is formed by providing a data decomposing means for dividing a large number of pixel data forming multi-gradation image data into blocks of a predetermined number to generate a large number of block data. A density calculating means for calculating each density data of a plurality of pixel data is provided, and a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data is provided for each block data,
If the difference calculation means for calculating the difference between the average data of the previous time and this time is provided, and the data comparison means for determining whether the difference of the average data is within the preset allowable range is provided, and if the difference is not within the allowable range Inserts an identifier indicating the adoption of the average data this time at the bottom of the gradation width index, and provides the first encoding means for generating compressed data by the average data, the gradation width index, and the code for each pixel data, If the difference is within the allowable range, an identifier indicating the adoption of the previous average data is inserted at the bottom of the gradation width index, and a second code that generates compressed data by this gradation width index and the code for each pixel data. A means for activating was provided.

According to a fifth aspect of the present invention, an identifier determining means for reading the identifier from the lowest of the gradation width index of the compressed data to determine the presence or absence of average data is provided. The first decoding means for generating the data is provided, and the second decoding means for generating the density data from the previous average data, the current gradation width index, and the code for each pixel data this time is provided when there is no average data.

According to a sixth aspect of the present invention, the block data is formed by providing a data decomposing means for dividing a large number of pixel data forming multi-gradation image data into blocks of a predetermined number to generate a large number of block data. A density calculating means for calculating each density data of a plurality of pixel data is provided, and a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data is provided for each block data,
If the difference calculation means for calculating the difference between the average data of the previous time and this time is provided, and the data comparison means for determining whether the difference of the average data is within the preset allowable range is provided, and if the difference is not within the allowable range Inserts an identifier indicating the adoption of the average data this time at the bottom of the gradation width index, and provides the first encoding means for generating compressed data by the average data, the gradation width index, and the code for each pixel data, If the difference is within the allowable range, an identifier indicating the adoption of the previous average data is inserted at the bottom of the gradation width index, and a second code that generates compressed data by this gradation width index and the code for each pixel data. If the average data is present, the density data is generated from the compressed data of this time when the average data is present and the average data is read. A first decoding means for providing, when there is no average data is provided a second decoding means for generating density data from the previous average data and the current gradation width index and sign of each current pixel data.

According to a seventh aspect of the present invention, the block data is formed by providing a data decomposing unit that divides a large number of pixel data forming multi-gradation image data into blocks of a predetermined number to generate a large number of block data. A density calculating means for calculating each density data of a plurality of pixel data is provided, and a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data is provided for each block data,
A difference calculating means for calculating the difference between the average data of the previous time and this time and the difference of the gradation width index is provided, and whether the difference of the average data and the difference of the gradation width index are within the respective preset allowable ranges. If both the average data and the difference of the gradation width index are not within the allowable range by providing a data comparison means for determining each, the combination of the gradation width index, the average data and the code for each pixel data A first encoding means for generating compressed data by adding an identifier indicating the adoption of data and an identifier indicating the adoption of the current gradation width index is provided, and the difference in the average data is out of the allowable range, and the difference in the gradation width index is If the compression data is within the allowable range, the average data and the code for each pixel data are combined, and the identifier indicating the adoption of the current average data and the identifier indicating the adoption of the previous gradation width index are added to the compressed data. Second encoding means for producing is provided,
If the difference of the average data is within the allowable range and the difference of the gradation width index is not within the allowable range, the combination of the gradation width index and the code for each pixel data is added to the identifier indicating the adoption of the previous average data and this time. A third coding means for generating compressed data by adding an identifier indicating the adoption of the gradation width index is provided, and when both the average data and the difference of the gradation width index are within the allowable range, the code for each pixel data is set. A fourth encoding means for generating compressed data by adding an identifier indicating adoption of the previous average data and an identifier indicating adoption of the previous gradation width index is provided.

According to the present invention, an identifier judging means for reading two identifiers from the compressed data and judging the presence or absence of each of the average data and the gradation width index is provided, and both the average data and the gradation width index are present. Is provided with a first decoding means for generating density data from the compressed data of this time, and if there is average data but no gradation width index, density is calculated from the average data of this time, the previous gradation width index and the code of each pixel data of this time. A second decoding unit for generating data is provided, and when there is no average data and there is a gradation width index, a third decoding for generating density data from the previous average data, the current gradation width index, and the code for each pixel data this time. Means is provided, and when neither average data nor gradation range index is present, density data is generated from previous average data, previous gradation range index, and code for each pixel data this time Fourth decoding It provided the stage.

According to a ninth aspect of the present invention, the block data is formed by providing a data decomposing means for generating a large number of block data by dividing a large number of pixel data forming multi-gradation image data into a predetermined number of blocks. A density calculating means for calculating each density data of a plurality of pixel data is provided, and a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data is provided for each block data,
A difference calculating means for calculating the difference between the average data of the previous time and this time and the difference of the gradation width index is provided, and whether the difference of the average data and the difference of the gradation width index are within the respective preset allowable ranges. If both the average data and the difference of the gradation width index are not within the allowable range by providing a data comparison means for determining each, the combination of the gradation width index, the average data and the code for each pixel data A first encoding means for generating compressed data by adding an identifier indicating the adoption of data and an identifier indicating the adoption of the current gradation width index is provided, and the difference in the average data is out of the allowable range, and the difference in the gradation width index is If the compression data is within the allowable range, the average data and the code for each pixel data are combined, and the identifier indicating the adoption of the current average data and the identifier indicating the adoption of the previous gradation width index are added to the compressed data. Second encoding means for producing is provided,
If the difference of the average data is within the allowable range and the difference of the gradation width index is not within the allowable range, the combination of the gradation width index and the code for each pixel data is added to the identifier indicating the adoption of the previous average data and this time. A third coding means for generating compressed data by adding an identifier indicating the adoption of the gradation width index is provided, and when both the average data and the difference of the gradation width index are within the allowable range, the code for each pixel data is set. , Adding an identifier indicating the adoption of the previous average data and an identifier indicating the adoption of the previous gradation range index, and providing a fourth encoding means for generating compressed data, reading the two identifiers from the compressed data and reading the average data And an identifier determining means for determining the presence or absence of each of the gradation width indexes, and a first decoding means for generating the density data from the compressed data of this time when both the average data and the gradation width index are present. When there is average data and no gradation width index, a second decoding means for generating density data from the current average data, the previous gradation width index, and the code for each pixel data this time is provided, and there is no average data and the gradation width index is present. If there is, the third decoding means for generating the density data from the previous average data, the current gradation width index, and the code for each pixel data of this time is provided, and if both the average data and the gradation width index are not present, A fourth decoding means for generating density data from the average data, the previous gradation width index, and the code for each pixel data this time is provided.

[0035]

According to the invention described in claim 1, when the average data and the gradation width index are calculated for each block data, the difference calculating means calculates the difference between the gradation width index between the previous time and this time, and the difference between the gradation width indexes. The data comparison means determines whether or not is within a preset allowable range. If the difference is not within the allowable range, the first encoding means inserts an identifier indicating the adoption of the gradation width index this time at the bottom of the average data, and the average data, the gradation width index, and the code for each pixel data To generate compressed data. If the difference is within the permissible range, the second encoding means inserts an identifier indicating the adoption of the previous gradation width index at the bottom of the average data, and compresses the compressed data by the average data and the code for each pixel data. To generate. Therefore, if the gradation width index is the same as the previous one, the gradation width index is not set in the compressed data, and an identifier indicating that the gradation width index is the same as the previous compressed data is set.

According to the second aspect of the present invention, when the identifier determining means reads the identifier from the bottom of the average data of the compressed data and determines the presence or absence of the gradation width index, if the gradation width index is present, When the first decoding means generates density data from the current compressed data and there is no gradation range index, the second decoding means uses the average data of this time, the previous gradation range index, and the code for each pixel data of this time. Generate concentration data. Therefore, if an identifier indicating that the gradation width index is the same as the previous one is set in the compressed data, the density data is generated by the previous gradation width index.

According to the third aspect of the present invention, when the average data and the gradation width index are calculated for each block data, the difference calculating means calculates the difference between the gradation width indexes of the previous time and this time, and the difference of the gradation width indexes. The data comparison means determines whether or not is within a preset allowable range. If the difference is not within the allowable range, the first encoding means inserts an identifier indicating the adoption of the gradation width index this time at the bottom of the average data, and the average data, the gradation width index, and the code for each pixel data To generate compressed data. If the difference is within the permissible range, the second encoding means inserts an identifier indicating the adoption of the previous gradation width index at the bottom of the average data, and compresses the compressed data by the average data and the code for each pixel data. To generate.

When the identifier judging means reads the identifier from the lowest of the average data of the compressed data and judges the presence / absence of the gradation width index, if the gradation width index exists, the first decoding means makes the current compression. Density data is generated from the data, and when there is no gradation width index, the second decoding means generates density data from the average data and the previous gradation width index.

Therefore, when the pixel data is encoded into the compressed data, if the gradation width index is the same as the previous one, it means that the gradation width index is not set in the compressed data and the gradation width index is the same as the previous one. The identifier is set. When decoding compressed data into density data, if an identifier indicating that the gradation width index is the same as the previous one is set in the compressed data, the density data is generated with the previous gradation width index.

According to the invention described in claim 4, when the average data and the gradation width index are calculated for each block data, the difference calculating means calculates the difference between the average data of the previous time and this time, and the difference of the average data is calculated in advance. The data comparison means determines whether or not it is within the set allowable range. If the difference is not within the allowable range, the first encoding means inserts an identifier indicating the adoption of the average data at this time at the lowest position of the gradation width index, and calculates the average data, the gradation width index, and the code for each pixel data. Generate compressed data. When the difference is within the allowable range, the second encoding means inserts an identifier indicating the adoption of the previous average data at the lowest position of the gradation width index, and compresses the compressed data by this gradation width index and the code for each pixel data. To generate. Therefore, if the average data is the same as the previous time, the average data is not set in the compressed data, and an identifier indicating that the average data is the same as the previous time is set.

According to the fifth aspect of the invention, when the identifier determining means reads the identifier from the lowest of the gradation width index of the compressed data and determines the presence or absence of average data, if there is average data, One decoding means generates density data from the current compressed data, and if there is no average data, the second decoding means uses the average data of the previous time, the gradation width index of this time, and the code of each pixel data of this time to generate the density. Generate data. Therefore, if an identifier indicating that the average data is the same as the previous time is set in the compressed data,
Density data is generated from the previous average data.

In the invention according to claim 6, when the average data and the gradation width index are calculated for each block data, the difference calculating means calculates the difference between the average data between the previous time and this time, and the difference between the average data is calculated in advance. The data comparison means determines whether or not it is within the set allowable range. If the difference is not within the allowable range, the first encoding means inserts an identifier indicating the adoption of the average data at this time at the lowest position of the gradation width index, and calculates the average data, the gradation width index, and the code for each pixel data. Generate compressed data. When the difference is within the allowable range, the second encoding means inserts an identifier indicating the adoption of the previous average data at the lowest position of the gradation width index, and compresses the compressed data by this gradation width index and the code for each pixel data. To generate.

When the identifier judging means reads the identifier from the lowest of the gradation width index of the compressed data and judges the presence / absence of the average data, if the average data exists, the first decoding means makes the current compression. If density data is generated from the data and there is no average data, the second decoding means
Density data is generated from the previous average data, the current gradation width index, and the code for each pixel data this time.

Therefore, when the pixel data is encoded into the compressed data, if the average data is the same as the previous time, the average data is not set in the compressed data, and an identifier indicating that the average data is the same as the previous time is set. To be done. When decoding the compressed data into the density data, if the compressed data has an identifier indicating that the average data is the same as the previous time, the density data is generated from the previous average data.

In the invention according to claim 7, when the average data and the gradation width index are calculated for each block data, the difference calculating means calculates the difference between the average data and the gradation width index between the previous time and this time. The data comparison means determines whether or not the difference between the average data and the difference between the gradation width indexes is within a preset allowable range. If both the average data and the difference of the gradation width index are not within the allowable range, the first encoding means adopts the average data of this time to the combination of the gradation width index, the average data, and the code for each pixel data. And an identifier indicating the adoption of the current gradation width index are added to generate compressed data. If the difference of the average data is not in the allowable range and the difference of the gradation width index is in the allowable range,
The second encoding means adds compressed data to the combination of the average data and the code for each pixel data with an identifier indicating the adoption of the average data this time and an identifier indicating the adoption of the previous gradation width index. To do. When the difference of the average data is within the allowable range and the difference of the gradation width index is not within the allowable range, the third encoding unit combines the gradation width index and the code for each pixel data with the previous average data. Compressed data is generated by adding an identifier indicating adoption and an identifier indicating adoption of the current gradation width index. When both the difference between the average data and the gradation width index are within the allowable range, the fourth encoding means adopts the identifier indicating the adoption of the previous average data and the previous gradation width index in the code for each pixel data. Compressed data is generated by adding the indicated identifier.

Therefore, if the gradation range index is the same as the previous one,
If the gradation width index is not set in the compressed data, an identifier indicating that the gradation width index is the same as the previous compressed data is set, and if the average data is the same as the previous time, the average data is not set in the compressed data, An identifier indicating that the average data is the same as the previous one is set.

According to the eighth aspect of the invention, the identifier determining means reads the two identifiers from the compressed data and determines the presence or absence of each of the average data and the gradation width index. When both the average data and the gradation width index are present, the first decoding means,
Density data is generated from the compressed data this time. When there is average data and no gradation width index, the second decoding means generates density data from the current average data, the previous gradation width index, and the code for each pixel data this time. If there is no average data and there is a gradation width index, the third decoding means generates density data from the previous average data, the current gradation width index, and the code for each pixel data this time. If both the average data and the gradation width index are absent, the fourth decoding means generates density data from the previous average data, the previous gradation width index, and the code for each pixel data this time.

Therefore, if an identifier indicating that the gradation range index is the same as the previous one is set in the compressed data,
If the density data is generated by the previous gradation width index, and the compressed data has an identifier indicating that the average data is the same as the previous time, the density data is generated by the previous average data.

In the ninth aspect of the present invention, when the average data and the gradation width index are calculated for each block data, the difference calculating means calculates the difference between the average data of the previous time and this time and the difference of the gradation width index. The data comparison means determines whether or not the difference between the average data and the difference between the gradation width indexes is within a preset allowable range. If both the average data and the difference of the gradation width index are not within the allowable range, the first encoding means adopts the average data of this time to the combination of the gradation width index, the average data, and the code for each pixel data. And an identifier indicating the adoption of the current gradation width index are added to generate compressed data. If the difference of the average data is not in the allowable range and the difference of the gradation width index is in the allowable range,
The second encoding means adds compressed data to the combination of the average data and the code for each pixel data with an identifier indicating the adoption of the average data this time and an identifier indicating the adoption of the previous gradation width index. To do. When the difference of the average data is within the allowable range and the difference of the gradation width index is not within the allowable range, the third encoding unit combines the gradation width index and the code for each pixel data with the previous average data. Compressed data is generated by adding an identifier indicating adoption and an identifier indicating adoption of the current gradation width index. When both the difference between the average data and the gradation width index are within the allowable range, the fourth encoding means adopts the identifier indicating the adoption of the previous average data and the previous gradation width index in the code for each pixel data. Compressed data is generated by adding the indicated identifier.

The identifier determining means reads the two identifiers from the compressed data and determines the presence or absence of each of the average data and the gradation width index. When both the average data and the gradation width index are present, the first decoding means generates density data from the current compressed data. When there is average data and no gradation width index, the second decoding means generates density data from the current average data, the previous gradation width index, and the code for each pixel data this time. If there is no average data and there is a gradation width index, the third decoding means generates density data from the previous average data, the current gradation width index, and the code for each pixel data this time. If both the average data and the gradation width index are absent, the fourth decoding means generates density data from the previous average data, the previous gradation width index, and the code for each pixel data this time.

Therefore, when the pixel data is encoded into the compressed data, if the gradation width index is the same as the previous one, the gradation width index is not set in the compressed data and the gradation width index is the same as the previous compressed data. If the average data is equal to the previous time, the average data is not set to the compressed data, and the identifier indicating that the average data is the same as the previous time is set. When decoding compressed data into density data, if the compressed data has an identifier indicating that the gradation range index is the same as the previous one, density data is generated by the previous gradation range index and If the identifier indicating that the average data is the same as the previous one is set, the density data is generated from the previous average data.

[0052]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. With respect to the digital copying machine 15 shown as the image processing apparatus in the present embodiment, the same parts as those of the digital copying machine 6 described above as the second conventional example use the same names and reference numerals and detailed description thereof will be omitted. .

FIG. 1 is an overall block diagram of the digital copying machine 15, FIG. 2 is a block diagram of a main portion, FIG. 3 is a front view showing image data, and FIG. 4 is a pixel data encoding and decoding by a conventional method. 5A is a schematic diagram showing a state where density data of block data is calculated, FIG. 5B is a schematic view showing compressed data, FIG. 5C is a schematic view showing density data, and FIG. FIG. 6 is a schematic diagram showing the decoding of the data, FIG. 6 is a schematic diagram showing a state in which an identifier is inserted at the bottom of average data
FIG. 7 is a flowchart showing a part of encoding, and FIG. 8 is a flowchart showing a part of decoding.

First, in the digital copying machine 15 of this embodiment, as shown in FIG. 1, a code compression / expansion unit 16 is provided between the first image storage unit 9 and the second image storage unit 10, As shown in FIG. 2, the code compression / expansion unit 16 includes a code compression unit 17 and a code expansion unit 18. As will be described in more detail below, the code compression unit 17 further compresses the compressed data encoded in the same manner as the conventional system as a part of the encoding of the proposed system. The code expansion unit 18
As a part of decoding of the compressed data of the proposed method, the compressed data compressed by the proposed method is expanded into compressed data similar to the conventional method.

As shown in FIG. 3, the image data 19 read by the digital copying machine 15 of this embodiment is formed by image data 20 such as a picture, image data 21 such as characters, blank image data 22 and the like. And has a multi-gradation as a whole. Then, the digital copying machine 15 of the present embodiment can encode the multi-gradation image data 19 into compressed data, and can decode the compressed data into image data.

Therefore, the digital copying machine 15 of the present embodiment.
Is a means for encoding the image data 19 into compressed data, as in the conventional digital copying machine 6 as in the encoding / decoding section 7.
Further, it has a data decomposing means, a data calculating means, and a data encoding means. Further, since the code compression unit 17 of the code compression / decompression unit 16 includes a difference calculation unit, a data comparison unit, and a data correction unit as various units for further compressing the compressed data, the data encoding unit and The data correction means implements a first encoding means and a second encoding means. Here, the configurations and functions of these various encoding means will be sequentially described below.

First, the encoding / decoding unit 7 sequentially encodes image data into compressed data, and sequentially stores this compressed data in the first image storage unit 9. At this time, as shown in FIG. 4A, the data decomposing means divides a large number of pixel data 23 forming the multi-gradation image data 20 into “4 × 4” blocks and a large number of block data 24. The density calculating means generates the density data Lij (16 bytes) of each of the plurality of pixel data 23 forming the block data 24. As shown in FIG. 4B, the data calculation means is
The maximum value Lmax of the density data Lij for each block data 24
And the minimum value Lmin to calculate the average data La (1 byte) and the gradation width index Ld (1 byte), and the data encoding means calculates the average data La, the gradation width index Ld and the pixel data 2
Compressed data (6 bytes) is generated by the code φij (4 bytes) for each 3.

The compression data thus generated is sequentially stored in the first image storage unit 9 by the encoding / decoding unit 7, so that the code compression / expansion unit 16 stores the compressed data from the first image storage unit 9. It is sequentially read and compressed, and stored in the second image storage unit 10.

At this time, as will be described later in detail with reference to FIG. 7, the difference calculating means calculates the difference between the gradation width index Ld between the previous time and the present time for the compressed data that is sequentially read out, and the data is calculated. The comparison means determines whether or not the difference between the gradation width indices Ld is within a preset allowable range. This judgment is actually realized by calculating the difference as an absolute value and comparing this with the threshold value T.

Therefore, as shown in FIG. 7 and FIG. 6, when the difference is not within the allowable range, the data correction means causes the least significant LSB (Least Significa) of the average data La of the compressed data.
nt Bit), a 1-bit identifier “0” indicating the adoption of the gradation width index Ld this time is inserted. If the difference is within the allowable range, the 1-bit identifier “1” indicating the adoption of the previous gradation width index Ld is inserted in the lowest LSB of the average data La, and the gradation width index Ld is deleted from the compressed data. Such deletion of the gradation width index Ld is actually performed by the code compression / expansion unit 1.
6 is realized by stopping transmission of the gradation width index Ld when transmitting compressed data from the first image storage unit 9 to the second image storage unit 10.

The compressed data generated by the data coding means of the coding / decoding unit 7 as described above is converted into the code compression / decompression unit 16 described above.
When the difference of the gradation width index Ld is not within the allowable range, the first encoding means corrects the identifier “0” indicating the adoption of the gradation width index Ld of this time to the average data La by the data correction means of The average data La, the gradation width index Ld, and the code φij for each pixel data 23 are inserted into the lowest LSB.
And generate compressed data. If the difference is within the allowable range, the second encoding means sets the previous gradation width index Ld.
The identifier "1" indicating the adoption of is the lowest L of the average data La.
The compressed data is generated from the average data La and the code φij for each pixel data 23.

Further, the digital copying machine 15 of this embodiment is
As means for restoring the compressed data compressed as described above to a state similar to the conventional compressed data, an identifier determining means,
The data decompression means is included in the code decompression unit 18 of the code compression / decompression unit 16, and as in the conventional digital copying machine 6, the coding / decoding unit 7 serves as means for decoding the compressed data into pixel data. It has a data decoding means. Therefore, the data expansion unit and the data decoding unit implement the first decoding unit and the second decoding unit.
Here, the configurations and functions of these various means for decoding will be sequentially described below.

First, the code compression / expansion unit 16 sequentially reads the compressed data from the second image storage unit 10, decompresses the compressed data, and then stores the compressed data in the first image storage unit 9. At this time, as shown in FIG. 8, the identifier judging means reads the identifier from the lowest LSB of the average data La of the compressed data, and judges the presence or absence of the gradation width index Ld based on whether it is "0" or "1". . When the compressed data has a gradation width index Ld, the data expansion means reads the gradation width index Ld and the code φij from the compressed data, and the average data L
It is stored in the first image storage unit 9 together with a. If the compressed data does not have the gradation width index Ld, the average data La and the code φij are read from this compressed data and stored in the first image storage unit 9 together with the previous gradation width index Ld. The code decompression unit 18 uses the previous gradation width index L as described above.
Since d'is used for data processing, it has a code buffer (not shown) for temporarily storing the gradation width index Ld.

As described above, the compressed data stored in the first image storage unit 9 has the same form as the conventional one. The data is sequentially read and decoded into density data Lij.

As described above, the data decoding means of the encoding / decoding section 7 decodes the compressed data expanded by the data expanding means of the code compression / expansion section 16, whereby the first encoding means converts the compressed data into compressed data. When there is the adjustment index Ld, the density data Lij is generated from the current compressed data, and when the compressed data does not have the gradation width index Ld, the current average data La and the previous gradation width index Ld are generated. The density data Lij is generated from the current code φij.

With such a configuration, in the digital copying machine 15 of this embodiment, when the image data 20 read from the document by the scanner unit 2 is compressed and stored in the second image storage unit 10, the image data 20 is stored. The encoding / decoding unit 7 encodes the compressed data, and the first image storage unit 9 temporarily stores the compressed data. The compressed data temporarily stored in the first image storage unit 9 is further compressed by the code compression / decompression unit 16 and stored in the second image storage unit 10.

Then, as described above, the second image storage unit 10
When the compressed data stored in the first image decoding unit is decoded and is printed out by the printer unit 5, the compressed data stored in the second image storage unit 10 is expanded by the code compression / expansion unit 16 to a state similar to the conventional one, and The one image storage unit 9 is temporarily stored. The compression data temporarily stored in the first image storage unit 9 is decoded into image data by the encoding / decoding unit 7, and the printer unit 5
To print on paper.

In the digital copying machine 15 of the present embodiment, when the gradation widths of a plurality of continuous block data 24 are equal, only one of the block data 24 has a gradation width index Ld.
Is set, and the gradation width index L is calculated from the other block data 24.
Delete d. Then, by inserting an identifier indicating that the gradation width index Ld of the previous block data 24 is adopted into the block data 24 from which the gradation width index Ld is deleted, compression is performed without lowering the reproducibility of the image data 19. Reduce the amount of data.

Here, in the digital copying machine 15 of this embodiment, the compressed data stored in the first image storage section 9 is compressed by the code compression / expansion section 16 and stored in the second image storage section 10 as in the conventional case. The image processing method to be stored will be described below based on the flowchart of FIG. 7.

First, the code compression unit 1 of the code compression / decompression unit 16
Reference numeral 7 sequentially reads the average data La of a plurality of compressed data and the gradation width index Ld from the first image storage unit 9. By calculating the absolute value of the difference between the previous gradation width index Ld ′ and the current gradation width index Ld, and comparing this with a threshold value T, the difference between the previous gradation gradation index Ld and the previous gradation width index Ld is within the allowable range. Judge whether or not.

At this time, if the absolute value of the difference between the gradation width indexes Ld is larger than the threshold value T and the difference between the gradation width indexes Ld between the previous time and this time is not within the allowable range, the adjacent block data 2
Since the gradation widths of 4 are largely different, the gradation width index Ld is stored in the second image storage unit 10 as in the conventional case.
A 1-bit identifier “0” indicating the adoption of the gradation width index Ld this time is set to the lowest LSB of the average data La, and this average data La is stored in the second image storage unit 10. Further, by reading the code φij of the compressed data from the first image storage unit 9 and storing it in the second image storage unit 10, the average data La is stored in the second image storage unit 10 as in the conventional case.
Compressed data including the gradation width index Ld and the code φij is stored.

On the other hand, if the absolute value of the difference between the gradation width indices Ld is smaller than the threshold value T and the difference between the gradation width indices Ld between the previous time and this time is within the allowable range, the adjacent block data 24
Since the gradation widths of are similar, the gradation width index L
Erase d without storing it in the second image storage unit 10.
A 1-bit identifier “1” indicating the adoption of the previous gradation width index Ld is set to the lowest LSB of the average data La, and this average data La is stored in the second image storage unit 10. Then, by reading the code φij of the compressed data from the first image storage unit 9 and storing it in the second image storage unit 10, the average data La and the code φij are stored in the second image storage unit 10.
Compressed data that consists of only and has a smaller capacity than before is stored.

Next, an image processing method of reading compressed data from the second image storage unit 10 by the code compression / expansion unit 16 and expanding the compressed data into a form similar to the conventional one, and storing this in the conventional and first image storage units 9 will be described. Will be described below with reference to the flowchart of FIG.

First, the code decompression unit 1 of the code compression / decompression unit 16
Reference numeral 8 sequentially reads the average data La of a plurality of compressed data from the second image storage unit 10, and determines whether the identifier located at the lowest LSB of this average data La is "0" or "1".

At this time, the identifier of the average data La is "0".
Then, since the gradation width index Ld exists in the compressed data, this gradation width index Ld is used as the second image storage unit 10.
Read from. The gradation width index Ld is stored in the code buffer and the previous gradation width index Ld ′ is updated to obtain the average data L
The value a and the gradation width index Ld are stored in the first image storage unit 9.
Further, the code φij of the compressed data from the second image storage unit 10
By reading and storing in the first image storage unit 9,
The average data L is stored in the first image storage unit 9 as in the conventional case.
Compressed data including a, the gradation width index Ld, and the code φij is stored.

On the other hand, if the identifier of the average data La is "1", there is no gradation width index Ld in the compressed data, so the previous gradation width index Ld 'is adopted as the current gradation width index Ld. .. The gradation width index Ld is stored in the first image storage unit 9 together with the average data La, the code φij of the compressed data is read from the second image storage unit 10 and stored in the first image storage unit 9. Then, the first image storage unit 9 stores the compressed data including the average data La, the gradation width index Ld, and the code φij as in the conventional case.

Since the digital copying machine 15 of this embodiment can reduce the entire capacity of compressed data as described above, the storage area of the second image storage unit 10 can be saved and the second image can be saved. The time required to store data in the storage unit 10 can be shortened. Moreover, since the compressed data in which the gradation width index Ld is omitted is set with an identifier indicating that the previous gradation width index Ld is adopted, it is possible to satisfactorily decode the compressed data with a reduced capacity. The reproducibility of the image data 19 does not deteriorate.

The reproducibility of the image data 19 in the image processing method of this embodiment will be verified below. First, in the case where the image data is encoded and decoded as in the conventional case, as shown in FIG.
As shown in FIG. 5, all of the plurality of block data 24 are encoded into compressed data composed of the average data La, the gradation width index Ld and the code φij, and this is decoded into the density data Lij for each pixel data 23. Image data 1 to be converted in this way
9 includes multi-valued image data 20 and binary image data 21.
Although the blank image data 22 exists, a large number of block data 24 having the same gradation width are continuous in the binary and blank image data 21 and 22. For example, in FIG. 4, the average data La of the _first block data 24 ₁ and the gradation width index L
Even if d and the second block data 24 ₂ are replaced, as shown in FIG. 5, the density data Lij to be decoded is equivalent to the case where it is not replaced.

That is, the digital copying machine 15 of the present embodiment.
Can reduce the volume of compressed data without lowering the reproducibility of the image data 19. In the image processing method of this embodiment, the more the gradation widths of the block data 24 are equal, the more the gradation width index Ld can be omitted.
The larger the occupied areas of 1 and 22 are, the better the capacity of compressed data can be reduced.

In the digital copying machine 15 of the present embodiment, the block data 24 is encoded into compressed data by the encoding / decoding unit 7 as in the conventional case, and this compressed data is compressed by the code compression / expansion unit 16. However, the present invention is not limited to the above embodiment, and it is possible to directly generate more compressed compressed data from the block data 24. Similarly, it is illustrated that the more compressed data is expanded by the code compression / expansion unit 16 and this compressed data is decoded into the block data 24 by the encoding / decoding unit 7. However, the present invention is not limited to the above embodiment. However, it is also possible to directly generate the block data 24 from more compressed data.

Further, in the digital copying machine 15 of the present embodiment, when the continuous block data 24 have the same gradation width, the gradation width index Ld is omitted from the second and subsequent compressed data, and the previous gradation width index Ld is omitted. It has been illustrated that the identifier indicating that is adopted is inserted into the average data La. But,
The present invention is not limited to the above embodiment, and similar effects can be obtained by exchanging the roles of the average data La and the gradation width index Ld in the data processing as described above.

In this case, the average data La of the previous time and this time
Is calculated by the difference calculation means, and the data comparison means determines whether or not the difference of the average data La is within a preset allowable range. If the difference is not within the allowable range, the first encoding means inserts an identifier indicating the adoption of the average data La this time at the bottom of the gradation width index Ld, and the average data La, the gradation width index Ld, and each pixel data are inserted. Compressed data is generated with the sign of. If the difference is within the allowable range, the second encoding means inserts an identifier indicating the adoption of the previous average data La into the lowest position of the gradation width index Ld,
Compressed data is generated by the gradation width index Ld and the code for each pixel data.

When decoding such compressed data,
The identifier determination unit reads the identifier from the lowest of the gradation width index Ld of the compressed data to determine the presence or absence of the average data La. If there is the average data La, the first decoding unit extracts the density data from the current compressed data. If there is no average data La, the second decoding means generates density data from the previous average data La, the current gradation width index Ld, and the code for each pixel data this time.

As described above, if the densities of the continuous block data 24 are equal, the average data La is not set in the second and subsequent compressed data, indicating that the average data La is the same as the previous one. Since the identifier is set,
The overall capacity of the compressed data can be reduced without lowering the reproducibility of the image data 19.

A second embodiment of the present invention will be described below with reference to FIGS. 9 to 16. Note that, regarding the present embodiment, the same parts and portions as those of the first embodiment are designated by the same names and reference numerals, and detailed description thereof will be omitted.

FIG. 9 is a schematic diagram showing a state where four block data 24 are continuous, FIG. 10 is a schematic diagram showing a state where eight identifiers are continuous, and FIG. 11 is a main part of four compressed data. 12 and 13 are flowcharts showing a part of the encoding, FIG. 14 and FIG.
Is a flowchart showing a part of decoding.

First, the digital copying machine 15 of this embodiment is
The hardware configuration is the same as that of the first embodiment, and the code compression / expansion unit 16 is used as various means for compressing compressed data.
In the code compression unit 17 of, the difference calculation means, the data comparison means,
Data correction means is provided, but the data correction means of the code compression / expansion portion 16 corrects the compressed data generated by the data encoding means of the encoding / decoding portion 7, whereby the first encoding means, the second The encoding means, the third encoding means, and the fourth encoding means are realized. Here, in these various encoding means, parts different from the first embodiment will be sequentially described below.

As will be described later in detail with reference to FIGS. 12 and 13, the difference calculating means calculates the difference between the average data La of the previous time and the current data of the compressed data read sequentially.
The difference between the gradation width indexes Ld of the previous time and this time is sequentially calculated, and the data comparison means determines whether the difference of the average data La is within a preset allowable range or whether the difference of the gradation width indexes Ld is preset. It is sequentially determined whether or not it is within the allowable range.

If both the difference between the average data La and the gradation width index Ld is not within the allowable range, the first encoding means uses the combination of the gradation width index Ld, the average data La and the code φij for the current average. The compressed data is generated by adding an identifier “0” indicating the adoption of the data La and an identifier indicating the adoption “0” of the current gradation width index Ld. Average data L
When the difference of a is not within the allowable range and the difference of the gradation width index Ld is within the allowable range, the second encoding unit combines the average data La and the code φij with the current average data L.
Compressed data is generated by adding an identifier indicating the adoption of a and an identifier indicating the adoption of the previous gradation width index Ld. When the difference of the average data La is within the allowable range and the difference of the gradation width index Ld is not within the allowable range, the third encoding means adds the combination of the gradation width index Ld and the code φij to the previous average data La. An identifier indicating adoption and the gradation width index L of this time
Compressed data is generated by adding an identifier indicating the adoption of d. When both the difference between the average data La and the gradation width index Ld are within the allowable range, the fourth encoding means assigns the code φij to
Compressed data is generated by adding an identifier indicating the previous adoption of the average data La and an identifier indicating the previous adoption of the gradation width index Ld.

In the digital copying machine 15 of this embodiment, the four blocks of data 24 are set as one set and the above-mentioned processing is executed. Therefore, the identifier handled by this set of processing is 1 byte in total. Therefore, FIG.
, The 2-bit identifier θ of the four compressed data
Together with the deletion information byte of 1 byte, and
As shown in, the gradation width index Ld, the average data La, and the code φij of the four compressed data are integrated. For this reason,
The code compression / decompression unit 17 stores a 2-bit buffer for temporarily storing a 2-bit identifier θ, a 1-byte buffer for temporarily storing deletion information bytes, a code buffer for temporarily storing four compressed data, and the number of times of data processing. A block counter for integrating is provided.

Further, the digital copying machine 15 of the present embodiment is
The code decompression unit 18 of the code compression / decompression unit 16 has an identifier determination unit and a data decompression unit as means for decompressing the compressed data compressed as described above. The data decoding means of the encoding / decoding unit 7 decodes the compressed data decompressed by the first decoding means, the second decoding means, the third decoding means, and the fourth decoding means. Here, in these various means for decoding, parts different from the first embodiment will be sequentially described below.

As will be described later in detail with reference to FIGS. 14 and 15, the identifier judging means reads the two identifiers from the compressed data to obtain the average data La and the gradation width index Ld.
Determine the presence or absence of each. When both the average data La and the gradation width index Ld are present, the first decoding means generates the density data Lij from the current compressed data. Average data La
If there is, and there is no gradation width index Ld, the second decoding means generates the density data Lij from the current average data La, the previous gradation width index Ld, and the current code φij. Average data L
When there is no a and there is a gradation width index Ld, the third decoding means
The density data Lij is generated from the previous average data La, the current gradation width index Ld, and the current code φij. When there is neither the average data La nor the gradation width index Ld, the fourth decoding means generates the density data Lij from the previous average data La, the previous gradation width index Ld, and the current code φij.

In such a configuration, the digital copying machine 15 of this embodiment has a plurality of continuous block data 24.
If the densities and gradation widths are the same, some block data 2
By deleting the average data La and the gradation width index Ld from 4, and adding an identifier indicating this, the image data 1
9 reduces the volume of compressed data without lowering the reproducibility.

Here, in the digital copying machine 15 of the present embodiment, the compressed data stored in the first image storage section 9 is compressed by the code compression / expansion section 16 and stored in the second image storage section 10 as in the conventional case. The image processing method to be stored will be described below based on the flowcharts of FIGS. 12 and 13.

First, as shown in FIG. 12, the code compression unit 17 of the code compression / decompression unit 16 sequentially reads the average data La and the gradation width index Ld of four compressed data from the first image storage unit 2, and 2 The bit identifier θ is initialized to “0”. Next, by calculating the absolute value of the difference between the previous average data La ′ and the current average data La, and comparing this with the threshold value T1, the difference between the average data La between the previous time and this time is within the allowable range. Judge whether or not.

At this time, if the absolute value of the difference between the average data La is larger than the threshold value T1 and the difference between the average data La between the previous time and this time is not within the allowable range, the average data La is stored in a predetermined position of the code buffer. . At this time, since the 1-bit identifier “0” indicating the adoption of the average data La is stored in the lower bit of the 2-bit identifier θ in advance, this is not changed. On the other hand, the absolute value of the difference between the average data La is smaller than the threshold value T1, and the average data La between the previous time and this time is
If the difference is within the allowable range, the average data La is erased without being stored in the code buffer, and the 1-bit identifier “1” indicating the adoption of the previous average data La is set to the lower bit of the 2-bit identifier θ. Set to.

Next, the absolute value of the difference between the previous gradation width index Ld 'and the current gradation width index Ld is calculated, and this is compared with the threshold value T2 to determine the gradation width index Ld between the previous time and this time. It is determined whether the difference is within the allowable range.

At this time, when the absolute value of the difference between the gradation width indices Ld is larger than the threshold value T2 and the difference between the previous and present gradation width indices Ld is not within the allowable range, the gradation width index Ld is set to a predetermined position in the code buffer. To temporarily store. At this time, the 1-bit identifier “0” indicating the adoption of the gradation width index Ld is 2
This is not changed because it is stored in the upper bits of the bit identifier θ in advance. On the other hand, when the absolute value of the difference between the gradation width indices Ld is smaller than the threshold value T2 and the difference between the previous and present gradation width indices Ld is within the allowable range, the gradation width index Ld
Is erased without being stored in the code buffer, and the 1-bit identifier “1” indicating the adoption of the previous gradation width index Ld is set to 2
It is set at a predetermined position of the upper bit of the bit identifier θ.

The code φ of the compressed data from the first image storage unit 9.
The contents of one compressed data are set in these buffers by reading ij and storing it in the code buffer and setting the 2-bit identifier θ in the deletion information byte as shown in FIG. Therefore, it is confirmed whether the block count is "4" or less, and if it is "4" or less, "1" is added to the block count to return to the initial state.

By repeating the data processing as described above, the block count becomes "4" when the contents of the four compressed data are set in the two buffers.
Therefore, when this is confirmed, the contents of the deletion information byte and the code buffer are copied to the second image storage unit 10, and the second image storage unit 10 has four capacity reductions as compared with the conventional case. Compressed data is stored.

After the completion of such data processing, the write address of the code buffer is initialized to "0",
By initializing the block count to "1" and returning to the initial state, the next four compressed data can be compressed.

Next, an image processing method for reading the compressed data from the second image storage unit 10 by the code compression / expansion unit 16 and expanding the compressed data in the same manner as the conventional one, and storing this in the conventional and first image storage units 9 will be described. The following description is based on the flowcharts of FIGS. 14 and 15.

First, the code expansion unit 1 of the code compression expansion unit 16
Reference numeral 8 reads the 1-byte identifier of the four compressed data from the second image storage unit 10, extracts the 2-bit identifier θ of the single compressed data from this, and extracts the 2-bit identifier θ.
, In turn, determines whether they are “00”, “01”, “10”, or “11”.

Therefore, if the identifier θ is “00”, both the average data La and the gradation width index Ld are present in the compressed data, so these are read from the second image storage section 10. If the identifier θ is “01”, only the gradation width index Ld is read from the second image storage unit 10, and if the identifier θ is “10”, only the average data La is read from the second image storage unit 10. If the identifier θ is none of the above, the identifier θ is “11” and the compressed data does not include both the average data La and the gradation width index Ld. No data is read from the storage unit 10.

Next, the average data La and the gradation width index Ld read out as described above are stored in the first image storage unit 9, the code φij of the compressed data is read from the second image storage unit 10, and the first image is read. By storing in the storage unit 9, compressed data including the average data La, the gradation width index Ld, and the code φij is stored in the first image storage unit 9 as in the conventional case.

Then, the above-described data processing is repeated until the block count reaches "4", so that the four compressed data corresponding to the deletion information bytes are stored in the first image storage section 9.

Since the digital copying machine 15 of this embodiment can reduce the entire capacity of compressed data as described above, the storage area of the second image storage unit 10 can be saved and the second image can be saved. The time required to store data in the storage unit 10 can be shortened. Moreover, since the omitted content of the data is added as the identifier θ, the compressed data having a reduced capacity can be properly decoded, and the reproducibility of the image data 19 does not deteriorate.

In the digital copying machine 15 of the present embodiment, the block data 24 is encoded into compressed data by the encoding / decoding unit 7 as in the conventional case, and this compressed data is compressed by the code compression / expansion unit 16. However, the present invention is not limited to the above embodiment, and it is possible to directly generate more compressed compressed data from the block data 24. Similarly, it is illustrated that the more compressed data is expanded by the code compression / expansion unit 16 and this compressed data is decoded into the block data 24 by the encoding / decoding unit 7. However, the present invention is not limited to the above embodiment. However, it is also possible to directly generate the block data 24 from more compressed data.

[0109]

According to the first aspect of the present invention, there is provided a data decomposing means for dividing a large number of pixel data forming multi-gradation image data into blocks of a predetermined number to generate a large number of block data. A density calculating means for calculating each density data of a plurality of pixel data to be formed is provided, and a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data for each block data is provided. A difference calculating means for calculating the difference between the gradation width index and the current time is provided, and a data comparing means for determining whether the difference of the gradation width index is within a preset allowable range is provided.
If the difference is not within the allowable range, an identifier indicating the adoption of the gradation width index this time is inserted at the bottom of the average data, and compressed data is generated by the average data, the gradation width index, and the code for each pixel data. If the difference is within the allowable range by providing the first encoding means, the identifier indicating the adoption of the previous gradation width index is inserted at the bottom of the average data, and the average data and the code for each pixel data are used for compression. By providing the second encoding means for generating the data, if the gradation width index is the same as the previous one, the gradation width index is not set in the compressed data and the gradation width index is the same as the previous compressed data. Since the identifier shown is set, the capacity of the compressed data can be reduced, and the time required to store the compressed data can be shortened.

According to a second aspect of the present invention, an identifier judging means for reading the identifier from the lowest order of the average data of the compressed data and judging the presence or absence of the gradation width index is provided. Provided is a first decoding means for generating density data, and a second decoding means for generating density data from the current average data, the previous gradation width index, and the code for each pixel data this time when there is no gradation width index. As a result, if the compressed data has an identifier indicating that the gradation range index is the same as the previous one, density data is generated by the previous gradation range index, so compression with some data deleted The data can be well decoded, and the time required to read the compressed data can be shortened.

According to the third aspect of the present invention, the block data is formed by providing a data decomposing means for dividing a large number of pixel data forming multi-gradation image data into a predetermined number of blocks to generate a large number of block data. A density calculating means for calculating each density data of a plurality of pixel data is provided, and a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data is provided for each block data,
The difference calculation means for calculating the difference between the gradation width indexes of the previous time and this time is provided, and the data comparison means for determining whether or not the difference of the gradation width indexes is within a preset allowable range is provided. If there is not, an identifier indicating the adoption of the gradation width index this time is inserted at the bottom of the average data, and the first encoding means for generating compressed data by the average data, the gradation width index, and the code for each pixel data. If the difference is within the allowable range, an identifier indicating the adoption of the previous gradation width index is inserted at the bottom of the average data, and compressed data is generated by the average data and the code for each pixel data. (2) An encoding means is provided, and an identifier determining means is provided to read the identifier from the lowest of the average data of the compressed data and determine the presence or absence of the gradation width index. By providing the first decoding means for generating, and if there is no gradation width index, by providing the second decoding means for generating the density data from the current average data, the previous gradation width index, and the code for each pixel data this time, When encoding pixel data into compressed data, if the gradation width index is the same as the previous time, the gradation width index is not set in the compressed data, and an identifier indicating that the gradation width index is the same as the previous time is set. Therefore, the capacity of compressed data can be reduced, the time required for storing compressed data can be shortened, and when decoding compressed data to density data, the gradation width index in the compressed data must be the same as the previous one. If the identifier that indicates that there is is set, since the density data is generated by the previous gradation width index, it is possible to satisfactorily decode the compressed data in which the data is partially deleted. It is possible to shorten the time required for reading.

According to the fourth aspect of the present invention, the block data is formed by providing a data decomposing means for dividing a large number of pixel data forming multi-gradation image data into blocks of a predetermined number to generate a large number of block data. A density calculating means for calculating each density data of a plurality of pixel data is provided, and a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data is provided for each block data,
If the difference calculation means for calculating the difference between the average data of the previous time and this time is provided, and the data comparison means for determining whether the difference of the average data is within the preset allowable range is provided, and if the difference is not within the allowable range Inserts an identifier indicating the adoption of the average data this time at the bottom of the gradation width index, and provides the first encoding means for generating compressed data by the average data, the gradation width index, and the code for each pixel data, If the difference is within the allowable range, an identifier indicating the adoption of the previous average data is inserted at the bottom of the gradation width index, and a second code that generates compressed data by this gradation width index and the code for each pixel data. If the average data is the same as the previous time, the average data is not set in the compressed data, and the identifier indicating that the average data is the same as the previous time is set, so that the capacity of the compressed data is set. Can be reduced, it is possible to shorten the time required for storing the compressed data.

According to a fifth aspect of the present invention, an identifier determining means for reading the identifier from the lowest of the gradation width index of the compressed data to determine the presence or absence of average data is provided. A first decoding means for generating data is provided, and if there is no average data, a second decoding means for generating density data from the previous average data, the current gradation width index, and the code for each pixel data this time is provided. If the compressed data has an identifier that indicates that the average data is the same as the previous time, the density data is generated from the previous average data, so it is possible to improve the compressed data with some data deleted. The data can be decrypted and the time required to read the compressed data can be shortened.

According to a sixth aspect of the present invention, the block data is formed by providing a data decomposing means for dividing a large number of pixel data forming multi-gradation image data into blocks of a predetermined number to generate a large number of block data. A density calculating means for calculating each density data of a plurality of pixel data is provided, and a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data is provided for each block data,
If the difference calculation means for calculating the difference between the average data of the previous time and this time is provided, and the data comparison means for determining whether the difference of the average data is within the preset allowable range is provided, and if the difference is not within the allowable range Inserts an identifier indicating the adoption of the average data this time at the bottom of the gradation width index, and provides the first encoding means for generating compressed data by the average data, the gradation width index, and the code for each pixel data, If the difference is within the allowable range, an identifier indicating the adoption of the previous average data is inserted at the bottom of the gradation width index, and a second code that generates compressed data by this gradation width index and the code for each pixel data. If the average data is present, the density data is generated from the compressed data of this time when the average data is present and the average data is read. When there is no average data, the second decoding means for generating the density data from the previous average data, the current gradation range index, and the code for each pixel data this time is provided. When encoding data into compressed data, if the average data is the same as the previous time, the average data is not set in the compressed data, and the identifier indicating that the average data is the same as the previous time is set. It is possible to reduce the storage capacity of the compressed data, reduce the time required to store the compressed data, and when decoding the compressed data into the density data, the compressed data must have an identifier that indicates that the average data is the same as the previous time. If set, density data is generated from the previous average data, so compressed data with some data deleted can be decoded well, and compressed data can be read. It is possible to shorten the time required for the out.

According to a seventh aspect of the present invention, the block data is formed by providing a data decomposing means for dividing a large number of pixel data forming multi-gradation image data into blocks of a predetermined number to generate a large number of block data. A density calculating means for calculating each density data of a plurality of pixel data is provided, and a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data is provided for each block data,
A difference calculating means for calculating the difference between the average data of the previous time and this time and the difference of the gradation width index is provided, and whether the difference of the average data and the difference of the gradation width index are within the respective preset allowable ranges. If both the average data and the difference of the gradation width index are not within the allowable range by providing a data comparison means for determining each, the combination of the gradation width index, the average data and the code for each pixel data A first encoding means for generating compressed data by adding an identifier indicating the adoption of data and an identifier indicating the adoption of the current gradation width index is provided, and the difference in the average data is out of the allowable range, and the difference in the gradation width index is If the compression data is within the allowable range, the average data and the code for each pixel data are combined, and the identifier indicating the adoption of the current average data and the identifier indicating the adoption of the previous gradation width index are added to the compressed data. Second encoding means for producing is provided,
If the difference of the average data is within the allowable range and the difference of the gradation width index is not within the allowable range, the combination of the gradation width index and the code for each pixel data is added to the identifier indicating the adoption of the previous average data and this time. A third coding means for generating compressed data by adding an identifier indicating the adoption of the gradation width index is provided, and when both the average data and the difference of the gradation width index are within the allowable range, the code for each pixel data is set. , If the gradation width index is the same as the previous time by adding the identifier indicating the adoption of the previous average data and the identifier indicating the adoption of the previous gradation width index and providing the fourth encoding means for generating the compressed data. For example, if the gradation width index is not set for the compressed data, an identifier indicating that the gradation width index is the same as the previous compressed data is set, and if the average data is the same as the previous time, the average data is set for the compressed data. Not, because an identifier indicating that the average data is the same as the previous time is set, it is possible to reduce the capacity of the compressed data, it is possible to shorten the time required for storing the compressed data.

According to the invention described in claim 8, there is provided an identifier judging means for reading two identifiers from the compressed data and judging the presence or absence of each of the average data and the gradation width index, and when both the average data and the gradation width index are present. Is provided with a first decoding means for generating density data from the compressed data of this time, and if there is average data but no gradation width index, density is calculated from the average data of this time, the previous gradation width index and the code of each pixel data of this time. A second decoding unit for generating data is provided, and when there is no average data and there is a gradation width index, a third decoding for generating density data from the previous average data, the current gradation width index, and the code for each pixel data this time. Means is provided, and when neither average data nor gradation range index is present, density data is generated from previous average data, previous gradation range index, and code for each pixel data this time Fourth decoding By providing the step, if the compressed data has an identifier indicating that the gradation range index is the same as the previous one, the density data is generated by the previous gradation range index, and the average data is added to the compressed data last time. If the identifier indicating that the data is the same as is set, the density data is generated from the previous average data, it is possible to satisfactorily decode the compressed data in which the data is partially deleted. The time required for reading can be shortened.

According to a ninth aspect of the present invention, the block data is formed by providing a data decomposing means for generating a large number of block data by dividing a large number of pixel data forming multi-gradation image data into blocks of a predetermined number. A density calculating means for calculating each density data of a plurality of pixel data is provided, and a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data is provided for each block data,
A difference calculating means for calculating the difference between the average data of the previous time and this time and the difference of the gradation width index is provided, and whether the difference of the average data and the difference of the gradation width index are within the respective preset allowable ranges. If both the average data and the difference of the gradation width index are not within the allowable range by providing a data comparison means for determining each, the combination of the gradation width index, the average data and the code for each pixel data A first encoding means for generating compressed data by adding an identifier indicating the adoption of data and an identifier indicating the adoption of the current gradation width index is provided, and the difference in the average data is out of the allowable range, and the difference in the gradation width index is If the compression data is within the allowable range, the average data and the code for each pixel data are combined, and the identifier indicating the adoption of the current average data and the identifier indicating the adoption of the previous gradation width index are added to the compressed data. Second encoding means for producing is provided,
If the difference of the average data is within the allowable range and the difference of the gradation width index is not within the allowable range, the combination of the gradation width index and the code for each pixel data is added to the identifier indicating the adoption of the previous average data and this time. A third coding means for generating compressed data by adding an identifier indicating the adoption of the gradation width index is provided, and when both the average data and the difference of the gradation width index are within the allowable range, the code for each pixel data is set. , Adding an identifier indicating the adoption of the previous average data and an identifier indicating the adoption of the previous gradation range index, and providing a fourth encoding means for generating compressed data, reading the two identifiers from the compressed data and reading the average data And an identifier determining means for determining the presence or absence of each of the gradation width indexes, and a first decoding means for generating the density data from the compressed data of this time when both the average data and the gradation width index are present. When there is average data and no gradation width index, a second decoding means for generating density data from the current average data, the previous gradation width index, and the code for each pixel data this time is provided, and there is no average data and the gradation width index is present. If there is, a third decoding means for generating density data from the previous average data, the current gradation width index, and the code for each pixel data this time is provided, and if both the average data and the gradation width index are not present, When the pixel data is encoded into the compressed data by providing the fourth decoding means for generating the density data from the average data, the previous gradation width index, and the code for each pixel data this time, the gradation width index is set to the previous value. Is equal to, the gradation width index is not set in the compressed data, an identifier indicating that the gradation width index is the same as the previous compressed data is set, and if the average data is equal to the previous time, the compressed data is Since the average data is not set and the identifier indicating that the average data is the same as the previous time is set, the capacity of the compressed data can be reduced and the time required for storing the compressed data can be shortened. When decoding compressed data into density data, if the compressed data has an identifier indicating that the gradation range index is the same as the previous one, density data is generated by the previous gradation range index and If the identifier indicating that the average data is the same as the previous one is set, the density data is generated from the previous average data.

[Brief description of drawings]

FIG. 1 is a block diagram showing a digital copying machine which is a first embodiment of an image processing apparatus of the present invention.

FIG. 2 is a block diagram showing a code compression / decompression unit.

FIG. 3 is a front view showing image data.

FIG. 4 is a schematic diagram showing a process of encoding and decoding image data.

FIG. 5 is a schematic diagram showing a process of decoding compressed data.

FIG. 6 is a schematic diagram showing average data.

FIG. 7 is a flowchart showing a process of compressing compressed data.

FIG. 8 is a flowchart showing a process of expanding compressed data.

FIG. 9 is a schematic diagram showing block data of a second embodiment.

FIG. 10 is a schematic diagram showing a deletion information byte.

FIG. 11 is a schematic diagram showing a main part of compressed data.

FIG. 12 is a flowchart showing a first half of a process of compressing compressed data.

FIG. 13 is a flowchart showing a latter half of the process of compressing compressed data.

FIG. 14 is a flowchart showing a first half of a process of expanding compressed data.

FIG. 15 is a flowchart showing the latter half of the process of expanding compressed data.

FIG. 16 is a block diagram showing a digital copying machine which is an image processing apparatus of a first conventional example.

17A is a schematic diagram showing a state where image data is decomposed into pixel data, and FIG. 17B is an explanatory diagram showing a state where pixel data is decomposed into block data.

FIG. 18 is a schematic diagram showing an algorithm in which the data encoding unit encodes density data into compressed data.

FIG. 19 is a block diagram showing a digital copying machine which is an image processing apparatus of a second conventional example.

FIG. 20 is a block diagram showing an encoding / decoding unit.

[Explanation of symbols]

15 Image processing device 19 image data 23 pixel data 24 block data 11 Data decomposition means La average data Ld gradation range index Lij concentration data φij code

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Claims (9)

(57) [Claims] 1. A data decomposing means for generating a large number of block data by dividing a large number of pixel data forming multi-gradation image data into a predetermined number of blocks, and a plurality of pixel data forming the block data. A density calculating means for calculating density data, a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data for each block data, and a difference of the gradation width index between the previous time and this time Difference calculating means, a data comparing means for judging whether or not the difference between the gradation width indexes is within a preset allowable range, and if the difference is not within the allowable range, an identifier indicating the adoption of the gradation width index at this time is set. When the difference is within the allowable range, the first encoding means is inserted at the bottom of the average data, and the average data, the gradation width index, and the code for each pixel data generate compressed data. In this case, a second encoding means for inserting an identifier indicating the adoption of the previous gradation width index at the bottom of the average data and generating compressed data by the average data and the code for each pixel data is formed. An image processing device characterized by: 2. An identifier judgment means for reading an identifier from the lowest of average data of compressed data and judging presence / absence of a gradation width index, and a density data is generated from compressed data of this time when the gradation width index exists. An image characterized by comprising: a decoding means; and a second decoding means for generating density data from the current average data, the previous gradation width index, and the code for each pixel data this time if there is no gradation width index. Processing equipment. 3. A data decomposing means for generating a large number of block data by dividing a large number of pixel data forming multi-gradation image data into blocks each having a predetermined number, and each of the plurality of pixel data forming the block data. A density calculating means for calculating density data, a data calculating means for calculating the average data and the gradation width index from the maximum value and the minimum value of the density data for each block data, and a difference of the gradation width index between the previous time and this time Difference calculating means, a data comparing means for judging whether or not the difference between the gradation width indexes is within a preset allowable range, and if the difference is not within the allowable range, an identifier indicating the adoption of the gradation width index at this time is set. When the difference is within the allowable range, the first encoding means is inserted at the bottom of the average data, and the average data, the gradation width index, and the code for each pixel data generate compressed data. In this case, an identifier indicating the adoption of the previous gradation width index is inserted at the bottom of the average data, and the average data and the code for each pixel data are used to generate compressed data. An identifier determining means for reading the identifier from the lowest of the average data to determine the presence / absence of a gradation width index, a first decoding means for generating density data from the current compressed data if a gradation width index exists, and a gradation width index An image processing apparatus comprising: a second decoding unit that generates density data based on the current average data, the previous tone width index, and the code for each pixel data of this time if there is none. 4. A data decomposing means for generating a large number of block data by dividing a large number of pixel data forming multi-gradation image data into a predetermined number of blocks, and each of the plurality of pixel data forming the block data. Density calculation means for calculating density data, data calculation means for calculating average data and gradation range index from maximum and minimum values of density data for each block data, and difference for calculating the difference between the previous and current average data If the difference is not within the allowable range, the calculation means and the data comparing means for determining whether the difference between the average data is within a preset allowable range, and if the difference is not within the allowable range, an identifier indicating the adoption of the average data this time is used as the gradation width index If the difference is within the allowable range, the first encoding means that inserts the compressed data into the lowest order and generates the compressed data by the average data, the gradation width index, and the code for each pixel data , A second encoding unit that inserts an identifier indicating the adoption of the previous average data at the lowest position of the gradation width index and generates compressed data by the gradation width index and the code for each pixel data. A characteristic image processing device. 5. An identifier judgment means for reading the identifier from the lowest of the gradation width index of the compressed data to judge the presence or absence of the average data, and a first decoding for generating density data from the compressed data of this time if the average data exists. An image processing apparatus comprising: a second decoding unit that generates density data from the previous average data, the current gradation width index, and the current code for each pixel data when there is no average data. . 6. A data decomposing means for generating a large number of block data by dividing a large number of pixel data forming a multi-gradation image data into blocks each having a predetermined number, and each of the plurality of pixel data forming the block data. Density calculation means for calculating density data, data calculation means for calculating average data and gradation range index from maximum and minimum values of density data for each block data, and difference for calculating the difference between the previous and current average data If the difference is not within the allowable range, the calculation means and the data comparing means for determining whether the difference between the average data is within a preset allowable range, and if the difference is not within the allowable range, an identifier indicating the adoption of the average data this time is used as the gradation width index If the difference is within the allowable range, the first encoding means that inserts the compressed data into the lowest order and generates the compressed data by the average data, the gradation width index, and the code for each pixel data , An identifier indicating the adoption of the previous average data is inserted at the bottom of the gradation width index, and second gradation means for generating compressed data by this gradation width index and the code for each pixel data, and the rank of the compressed data An identifier determining unit that reads the identifier from the lowest of the adjustment index to determine the presence or absence of average data, a first decoding unit that generates density data from the compressed data of this time if there is average data, and an average data if there is no average data. An image processing apparatus comprising: a second decoding unit that generates density data from previous average data, a current gradation width index, and a code for each pixel data of this time. 7. A data decomposing means for generating a large number of block data by dividing a large number of pixel data forming multi-gradation image data into blocks each having a predetermined number, and each of a plurality of pixel data forming the block data. Density calculation means for calculating density data, data calculation means for calculating average data and gradation width index from maximum and minimum values of density data for each block data, difference between average data between previous time and this time and gradation width index Difference calculating means for calculating the difference between the average data and the gradation width index, and a data comparing means for judging whether or not the difference between the average data and the difference between the gradation width indexes are within preset allowable ranges. If both of the index differences are not within the allowable range, a combination indicating the gradation width index, the average data, and the code for each pixel data is used to identify the adoption of the average data this time. If the difference between the average encoding data and the first encoding means for generating the compressed data is not within the allowable range and the difference between the gradation width indices is within the allowable range, Second encoding means for generating compressed data by adding an identifier indicating the adoption of the average data this time and an identifier indicating the adoption of the previous gradation width index to a combination of the average data and the code for each pixel data If the difference of the average data is within the allowable range and the difference of the gradation width index is not within the allowable range, the combination of the gradation width index and the code of each pixel data is added to the identifier indicating the adoption of the previous average data and If both the third encoding means for generating compressed data by adding an identifier indicating the adoption of the gradation width index this time and the difference between the average data and the gradation width index are within the allowable range, the code for each pixel data An image processing apparatus characterized by adding an identifier indicating the adoption of identifier and previous tone width index indicating the adoption of the previous average data, a fourth encoding means for generating compressed data, in that it consists of. 8. An identifier determining means for reading two identifiers from the compressed data to determine the presence / absence of each of the average data and the gradation width index, and the density from the current compressed data when both the average data and the gradation width index are present. First decoding means for generating data, and second decoding means for generating density data from the average data of this time, the previous gradation width index and the code for each pixel data of this time when there is average data and no gradation width index If there is no average data and there is a gradation width index, a third decoding means for generating density data from the previous average data, the current gradation width index, and the code for each pixel data this time, the average data and the gradation width index. If both are not present, a fourth decoding means for generating density data from the previous average data, the previous gradation width index, and the code for each pixel data this time, is included. Processing apparatus. 9. A data decomposing means for generating a large number of block data by dividing a large number of pixel data forming multi-gradation image data into blocks each having a predetermined number, and each of the plurality of pixel data forming the block data. Density calculation means for calculating density data, data calculation means for calculating average data and gradation width index from maximum and minimum values of density data for each block data, difference between average data between previous time and this time and gradation width index Difference calculating means for calculating the difference between the average data and the gradation width index, and a data comparing means for judging whether or not the difference between the average data and the difference between the gradation width indexes are within preset allowable ranges. If both of the index differences are not within the allowable range, a combination indicating the gradation width index, the average data, and the code for each pixel data is used to identify the adoption of the average data this time. If the difference between the average encoding data and the first encoding means for generating the compressed data is not within the allowable range and the difference between the gradation width indices is within the allowable range, Second encoding means for generating compressed data by adding an identifier indicating the adoption of the average data this time and an identifier indicating the adoption of the previous gradation width index to a combination of the average data and the code for each pixel data If the difference of the average data is within the allowable range and the difference of the gradation width index is not within the allowable range, the combination of the gradation width index and the code of each pixel data is added to the identifier indicating the adoption of the previous average data and If both the third encoding means for generating compressed data by adding an identifier indicating the adoption of the gradation width index this time and the difference between the average data and the gradation width index are within the allowable range, the code for each pixel data A fourth coding means for generating compressed data by adding an identifier indicating the adoption of the previous average data and an identifier indicating the adoption of the previous gradation width index, and reading the two identifiers from the compressed data An identifier judging means for judging the presence or absence of each gradation width index, a first decoding means for generating density data from the current compressed data when both the average data and the gradation width index are present, and the gradation width index having the average data If there is no average data, the second decoding means for generating density data from the previous gradation width index and the code for each pixel data of this time, and if there is no average data and there is a gradation width index, the previous average data And the third decoding means for generating the density data from the current gradation width index and the code for each pixel data this time, and the previous average data when neither the average data nor the gradation width index is present. The image processing apparatus comprising: the fourth decoding means for generating density data from the previous sign of tone width index and each current pixel data, in that it consists of.