JP3347944B2 - Image encoding method and apparatus - 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 encoding method for compressing and storing image data by block encoding in an image processing device or the like, and an image encoding device for implementing the method.

[0002]

2. Description of the Related Art In an image processing apparatus such as a digital copying machine, for example, image data is compressed and stored in an image data storage section by block coding. An area determination signal is also embedded and stored in a compressed signal.

[0003] Taking a digital copying machine as an example, FIG.
A description will be given with reference to FIG. FIG. 8 is a block diagram showing a schematic configuration of an example of a conventional digital copying machine.
FIG. 9 is a block diagram illustrating a configuration of an image output unit in FIG. 8.

A copier that handles image data as a digital signal includes a scanner 101, an A / D converter 102, an image processor 103, and an image output unit 104, as shown in FIG.
It is mainly composed of The scanner 101 reads image data, and the A / D converter 102 converts the image data into a digital signal. The image processing unit 103 performs image processing such as gamma conversion and image quality correction on the digital signal of the image data from the A / D conversion unit 102, and the image output unit 104 prints the image data on a transfer material such as paper for each pixel. And output the image.

[0005] As shown in FIG.
LD (laser diode) unit 202, cylinder lens 203, polygon mirror 204, fθ lens 20
5 and a photoconductor 206. That is, a laser beam is output from the LD unit 202 in response to a signal from the image processing unit 103. This laser beam
The laser beam applied to the polygon mirror 204 through the cylinder lens 203 and reflected by the polygon mirror 204 is applied to the photoconductor 206 through the fθ lens 205. Here, by rotating the polygon mirror 204 and scanning the laser light, image data is written on the photoconductor 206 line by line.

FIG. 10 is a diagram for explaining the relationship between the read gradation and the reproduced image. In general, the control of the pixel density is performed by changing the density value of each pixel with respect to the density value of each pixel as shown in FIG. This is performed by changing the pulse width of the signal for controlling the output width. FIG. 2A shows the read gray scale, and FIG. 2B shows the pulse assignment of a signal for controlling the laser output in accordance with the read gray scale in ns (nanoseconds). FIG. 10C shows a waveform of a pulse generated according to the pulse allocated in FIG. 10B, and FIG. 10D shows a state of a reproduced image. In the method of simply allocating the pulse according to the read gradation and controlling the pulse width, pixels may be separated at a thin line or a character edge portion perpendicular to the main scanning direction and may be conspicuous as noise.

In such a case, noise is reduced by adding the phase information for each pixel and changing the position of the pixel as shown in FIG. 11 for explaining the relationship between the read gradation and the reproduced image together with the phase information. Can be reduced. 2A shows the read gradation, FIG. 2B shows the pulse assignment in ns, and FIG. 1C shows the pulse waveform generated according to the pulse assigned in FIG. 1B. (D) shows the state of the reproduced image, and (e) shows the added phase information.

Since the control of the addition of the phase information as shown in FIG. 11E is changed depending on the edge portion of the image, as shown in FIG. 12 for explaining the position of the phase determined by the arrangement of the pixels. It is determined by looking at the state of the pixels before and after the pixel to which the phase information is added. That is, as shown in FIG. 2A, when a pixel to which phase information is added is D ₀ ,
The front of the pixels D _1, the rear of pixels and D _-1, if D _-1 -D _1> 64, the phase on the front side as (b), | if ≦ 64 | D _-1 -D ₁ For example, the phase may be set at the center as shown in (c), and if D _-1 -D ₁ <64, the phase may be set at the rear side as shown in (d).

By the way, in such a digital copying machine, in a picture part other than a character part and a halftone dot part, a large number of pseudo gray levels are shown with a small number of output gray levels. It is common to use a gradation process such as a method. For this reason, when the above-described phase processing is performed at the time of output, the image quality can be improved in a line or a character image portion, but when such processing is performed in a picture portion or a halftone portion other than a character, gradation processing is performed. It is better to fix the phase information because the arrangement of the pixels is distorted and the image quality is deteriorated. For this reason, a method of changing the phase in accordance with the density information in the line or character image portion as shown in FIG. 12, and a method of simply changing the pulse width in a fixed phase in a picture portion or a halftone portion where other gradation processing is performed. For example, it is necessary to switch the method depending on the image. Therefore, it is necessary to determine the character area of the image. Therefore, the image processing unit 103 performs the area determination, and switches the processing of the character part, the other picture part, and the halftone part according to the determination signal.

FIG. 13 is a block diagram showing the configuration of the image processing unit 103. The image processing unit 103 includes a character area determination unit 601, a gradation processing unit 602, and a phase output unit 603.
It is composed of That is, the image signal converted into a digital signal from the A / D conversion unit 102 is input to the character region determination unit 601 where region determination is performed using pattern matching or the like. Now, assuming that the image to be read is a document 700 as shown in FIG. 14, the determination information that the character region 702 of the document 700 is 1 and the region including the picture region 701 is 0 is added for each pixel. The determination information is used as a determination signal as the gradation processing unit 602 and the phase output unit 6.
03 is input. The gradation processing unit 602 switches the gradation processing, and the phase output unit 603 switches the phase control. Based on the signal of the phase output unit 603, the image output unit 104 switches the phase and outputs an image optimal for the image area.

As described above, in a copying machine that handles an image as a digital signal, the image can be stored in a memory . If the image data can be stored in the memory, the image once captured can be used many times, and the input / output address can be changed to perform processing / editing such as image rotation. However, if the amount of information of the image is large and stored in the memory as it is, a large amount of memory is required, and the unit cost of the memory is high, so that the overall cost becomes high. Therefore, if the image data is compressed and stored in the memory, the amount of memory can be reduced and the cost can be reduced. Therefore, the image data is compressed by an image data compression method such as a block coding method.

FIG. 15 is a diagram for explaining the relationship between an original image and a pixel block in the block coding system, and FIG. 16 is a diagram showing an example of a compression algorithm by the lock coding system. That is, in the block coding method as an image data compression method, as shown in FIG. 15, an original image is decomposed into blocks, and a 1-byte density value L in a block is obtained.
ij is compressed by the algorithm shown in FIG. 16 into an average value La (1 byte), a gradation width index Ld (1 byte), and a gradation quantization code φji (2 bits × 16) for each pixel. . Qj in FIG. 16 is a representative quantization value at the time of decoding, and is a density value assigned to each code at the time of decoding as follows.

Φij = 11 → Q1 = La + 3/4 Ld φij = 10 → Q2 = La + 1/4 Ld φij = 00 → Q3 = La−1 / 4 Ld φij = 01 → Q4 = La−3 / 4 Ld Depending on the encoding method, before encoding, 4
The data amount of 16 bytes of the × 4 pixel block is calculated as φij (16 × 2 bits) + La (1 byte) + Ld (1
(Byte) = 6 bytes, and compression can be performed to a data amount of 3/8.

[0014]

When a copying machine having a writing unit for performing the above-described phase control is provided with an image storage unit for compressing image data and storing an image in a memory, a character area is determined. There is a drawback that the information of the above-described character area determination signal is required in addition to the compressed image data, and the memory must be increased accordingly.

The present invention has been made in view of such circumstances of the prior art, and a first object of the present invention is to incorporate a region determination signal into image compression data according to a block coding method, thereby obtaining the data of the region determination signal. It is an object of the present invention to provide an image coding method that absorbs the amount and prevents an increase in the amount of memory for a region determination signal.

A second object of the present invention is to provide an image coding apparatus which absorbs the data amount of the area judgment signal and prevents an increase in the amount of memory for the area judgment signal.

[0017]

According to a first aspect of the present invention, there is provided an image encoding method comprising the steps of decomposing each of multi-tone pixel data forming image data into a predetermined number. To generate block data, and for each pixel of the decomposed block data, encode the density data into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index. It is determined whether or not the image is a character image, and based on the determination result, a binary area determination signal is output for each pixel. If the area determination signal is a determination signal of a character area in the block data, 0 is set. Is inserted into the least significant bit of one of the average data of the compressed data and the gradation width index when a determination signal other than the character area is included in the block data, and Size If a signal is characterized by inserting a region determination signal for each pixel in the low-order bit of the gradation quantization code.

In order to achieve the first object, the image encoding method of the second means generates block data by decomposing each of the multi-gradation pixel data forming the image data into a predetermined number. Then, for each pixel of the decomposed block data, the density data is encoded into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index,
It is determined whether or not the image data is a character image, and based on the determination result, a binary area determination signal is output for each pixel. In the case of a signal, 0 is inserted into the least significant bit of one of the average data of the compressed data and the gradation width index, and 1 is inserted in the case of including a character area determination signal in the block data. When a determination signal of a character area is included, an area determination signal of each pixel is inserted into lower bits of the gradation quantization code.

In order to achieve the first object, the image encoding method of the third means generates block data by decomposing each of multi-tone pixel data forming image data into a predetermined number. Then, for each pixel of the decomposed block data, the density data is encoded into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index,
It is determined whether or not the image data is a character image, and based on the determination result, a binary area determination signal is output for each pixel, and the area determination signals are all character area determination signals in the block data. , A 2-bit signal 01 is used in the block data if it is a determination signal other than a character area, and 2 if the determination signal is a mixture of a character area and a non-character area in the block data. The bit signal 11 is inserted into the lower two bits of one of the average data of the compressed data and the gradation width index, or the least significant bit of both of the average data and the gradation width index, one bit at a time and inserted. When a character area and a determination signal other than a character area are mixed in the data, an area determination signal for each pixel is inserted into the lower bits of the gradation quantization code.

In order to achieve the second object, the image coding apparatus of the fourth means generates block data by decomposing each of the multi-gradation pixel data forming the image data into a predetermined number. And data for encoding the density data for each pixel of the block data decomposed by the data decomposing means into compressed data comprising a 2-bit gradation quantization code, average data and a gradation width index. Encoding means; image determination means for determining whether the image data is a character image; and area determination data output for outputting a binary area determination signal for each pixel based on the determination result of the image determination means Means, if the area determination signal output by the area determination data output means is a determination signal of a character area in the block data, 0 is determined, and the area other than the character area is determined in the block data. In the case of including the signal, 1 is inserted in the least significant bit of one of the average data and the gradation width index of the compressed data output from the data encoding means, When a determination signal other than a character area is included, a pixel unit area determination bit inserting means for inserting an area determination signal for each pixel into lower bits of the gradation quantization code is provided.

In order to achieve the second object, the image encoding apparatus of the fifth means generates block data by decomposing each of the multi-gradation pixel data forming the image data into a predetermined number. And data for encoding the density data for each pixel of the block data decomposed by the data decomposing means into compressed data comprising a 2-bit gradation quantization code, average data and a gradation width index. Encoding means; image determination means for determining whether the image data is a character image; and area determination data output for outputting a binary area determination signal for each pixel based on the determination result of the image determination means Means, and if the area determination signal output by the area determination data output means is a determination signal other than a character area in the block data, 0 is determined, and the area determination signal is determined in the block data. In the case of including the signal, 1 is inserted in the least significant bit of one of the average data and the gradation width index of the compressed data output from the data encoding means, When a determination signal of a character area is included, a pixel unit area determination bit inserting means for inserting an area determination signal for each pixel into lower bits of the gradation quantization code is provided.

In order to achieve the second object, the image coding apparatus of the sixth means generates block data by decomposing each of the multi-gradation pixel data forming the image data into a predetermined number. And data for encoding the density data for each pixel of the block data decomposed by the data decomposing means into compressed data comprising a 2-bit gradation quantization code, average data and a gradation width index. Encoding means; image determination means for determining whether the image data is a character image; and area determination data output for outputting a binary area determination signal for each pixel based on the determination result of the image determination means Means, and when the area determination signal output by the area determination data output means is a determination signal of a character area in the block data, a 2-bit signal 00 is output in the block data. The 2-bit signal 01 in the case of the determination signal other than character region, the 2-bit signal when the determination signal other than the character region and the character region in the block data are mixed 1
1 is the lower 2 bits of one of the average data of the compressed data output by the data encoding means and the gradation width index, or
In the case where an in-block area determination bit insertion unit that inserts one bit at a time into the least significant bit of both the average data and the gradation width index and a determination signal other than a character area and a non-character area are mixed in the block data, And a pixel unit area determination bit inserting means for inserting an area determination signal for each pixel into lower bits of the gradation quantization code.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a digital copying machine will be described below with reference to FIGS. FIG. 1 is a block diagram illustrating a schematic configuration of a digital copying machine according to an embodiment of the present invention, FIG. 2 is a block diagram illustrating a configuration of an image storage unit in FIG. 1, and FIG. 3 illustrates an example of storing block area information bits. FIG. 4 is a diagram for explaining a plurality of states of a plurality of squares in a block, FIG. 5 is a diagram for explaining another example of a plurality of states of a square in a block, and FIG. 6 is a block area. FIG. 7 is a diagram for explaining another example of storage of information bits, and FIG. 7 is a diagram for explaining still another example of a plurality of masquerade states in a block.

First, the configuration of the digital copying machine will be described with reference to FIGS. The copying machine according to this embodiment includes a scanner 1201, an A / D converter 1202, and an image processor 1
203, character area determination unit 1204, gradation processing unit 120
5. Image storage unit 1206, two signal switching units 120
7, 1208, a phase output unit 1209, and an image output unit 1210. Scanner 120
1. The configurations of the A / D conversion unit 1202, image processing unit 1203, character area determination unit 1204, gradation processing unit 1205, phase output unit 1209, and image output unit 1210 are the same as the corresponding configurations in the above-described conventional example. Is fine.

The construction and operation of the copying machine will be described in more detail. First, a case where the image data is output as it is without storing the image data in the image storage unit 1206 will be described.
The conversion unit 1202 converts the image data into a digital signal. The image processing unit 1203 performs image processing such as gamma conversion on the digital signal of the image data from the A / D conversion unit 102, and based on the output, determines the character area in the character area determination unit 1204, based on the determination signal. Key processing unit 1205
Switches the gradation processing. Here, the signal switching unit 1
207 is connected to the B side, and image data is sent to the image output unit 1210. In the image output unit 1210, the phase output unit 12
In accordance with the 09 phase data, printing is performed by switching the phase for each pixel, and an image is output. Signal switching unit 1208
Is connected to C, the phase data is input directly to the phase output unit 1209 with an area determination signal for identifying the character area obtained by the character area determination unit 1204, and the phase output unit 1209 outputs the image data and the area. The phase data is output according to the determination signal.

Next, a case where image data is compressed and stored in the image storage unit 1206, decoded, and output will be described. The processing up to the scanner 1201, the A / D conversion unit 1202, the image processing unit 1203, the character area determination unit 1204, and the gradation processing unit 1205 is performed by the image storage unit 1206 described above.
Is the same as when not using The image data from the gradation processing unit 1205 is stored after being compressed by the image storage unit 1206. Also, the area determination signal from the character area determination unit 1204 is compressed and stored in the image storage unit 1206. When the image storage unit 1206 stores information for one page, the image data and the area determination signal are expanded and output. At this time, by switching the signal switching unit 1207 to the A side, the image data is transferred to the phase output unit 1209 and the image output unit 1.
Sent to 210. On the other hand, the signal switching unit 1208
By switching to the side, the area determination signal from the image storage unit 1206 is sent to the phase output unit 1209. The phase output unit 1209 outputs the phase data to the image output unit 1210 based on the image data and the area determination signal. Image output unit 1
At 210, printing is performed by switching the phase for each pixel based on the phase data from the phase output unit 1209, and an image is output.

The present invention is characterized in that the code data and the area determination signal are combined in the image storage unit 1206, and this feature will be described in detail with reference to FIG. The image storage unit 1206 includes a 4-line FIFO (first-in first-out) unit 1301, an encoding unit 1302, a binary 4-line FIFO unit 1303, an area determination signal combining unit 1304,
And a memory 1305. The image data output to the image storage unit 1206 has four lines F
Once the data for four lines is stored in the IFO 1301, the data is encoded by the encoding unit 1302 for each 4 × 4 pixel block, and the data of La, Ld and φij are output.
On the other hand, the area determination signal is output from the binary 4-line FIFO unit 130.
After the signals for four lines are stored in 3, an area determination signal for each 4 × 4 pixel block is input to the area determination signal synthesis unit 1304, and the area determination signal is output from the encoding unit 1302 in block units. Combined with data. The synthesis is performed for each 4 × 4 pixel block.
As shown in (a) and (b) of FIG. 4, the area signal of the character area is set to 1 and the area signal of the other areas is set to 1 as the area determination signal in the 4 × 4 square. As described above, in the case of a block of 4 × 4 pixels and all of the character area, the area information bit b0 in the block is set to b0 = 0. In this case, the 2-bit gradation quantization code φij for each pixel is stored in the memory 1305 as it is. Is stored in Also, as shown in FIG. 4B, when a non-character area signal 0 is included in an area signal in a block of a block of 4 × 4 pixels, the area information bit b0 in the block is set to 1 and two bits for each pixel are set. Is replaced by the area determination signal at the corresponding position. The intra-block area information bit b0 is L
It is stored in the least significant bit of one byte of a or Ld as shown in FIG. In FIG. 3, the right end is the least significant bit and the left end is the most significant bit. Thus, if the in-block area information bit b0 is stored in the least significant bit, there is almost no effect on the decoded image. By inserting the area determination signal in this manner, the area signal can be combined with the code data without increasing the data amount. However, according to this method, when a block of 4 × 4 pixels includes a non-character area in an area signal in the block, the gradation quantization code φij has only 1-bit information, so that the image quality of a part other than the character is reduced. It may be slightly deteriorated, and it can be said that this method gives priority to the image quality of characters.

Next, a method of giving priority to image quality other than characters will be described. The only difference from the above-described method of prioritizing the image quality of characters is the processing of the area determination signal synthesizing unit 1304, and only that part will be described with reference to FIGS. In FIG. 5, the area signal of the character area is set to 1 and the area signal of the other areas is set to 1 as the area determination signal in the 4 × 4 square, and as shown in FIG. If all the blocks are non-character areas, the in-block area information bit b0 = 0 is set. In this case, the 2-bit gradation quantization code φij for each pixel is stored in the memory 1305 as it is. Also, as shown in FIG. 5B, when a region signal in a block of 4 × 4 pixels includes a character region,
It is assumed that the intra-block area information bit b0 = 1, and 2
The lower one bit of the bit gradation quantization code φij is replaced with the area determination signal at the corresponding position. The intra-block area information bit b0 is stored in the least significant bit of one byte of La or Ld as shown in FIG. By inserting the area determination signal in this manner, the area signal can be combined with the code data without increasing the data amount. However, according to this method, when the area signal in the block is a 4 × 4 pixel block and includes a character area, the gradation quantization code φij has only 1-bit information, so the image quality of the character area part is slightly degraded. Therefore, it can be said that this method gives priority to the image quality of a picture area and a halftone dot area other than characters.

Next, instead of giving priority to either the image quality of the character or the non-character area as in the above-described method, the degradation caused by the synthesis of the area determination signal is made uniform in the character and non-character areas to determine the area. A method for synthesizing signals will be described.
This method differs from the above-described method only in the processing of the area determination signal combining unit 1304, and only that part will be described with reference to FIG. In FIG. 7, the area signal of the character area is set to 1 and the area signal of the other areas is set to 1 as the area determination signal in the 4 × 4 square, and as shown in FIG.
In the case of a 4-pixel block and all character regions, 2-bit in-block region information bits b1 = 0 and b0 = 0. In this case, a 2-bit gradation quantization code φij for each pixel is
It is stored in the memory 1305 as it is. As shown in FIG. 7B, in the case of a block of 4 × 4 pixels and all non-character areas, a 2-bit area information bit b1 in the block
= 0, b0 = 1, and also in this case, the 2-bit gradation quantization code φij for each pixel is stored in the memory 1305 as it is. Next, as shown in FIG. 7C, when the area signal in the block is a 4 × 4 pixel block in which a character area and a non-character character area are mixed, a 2-bit area information bit b1 = 1 in the block , B0 = 1, and the lower 1 bit of the 2-bit gradation quantization code φij for each pixel is replaced with the area determination signal at the corresponding position. As shown in FIG. 6, the in-block area information bits b1 and b0 are stored in the least significant two bits of one byte of La or Ld, or are divided into the least significant one bits of both La and Ld. . In this way, this inserting a region determination signal, without increasing the amount of data, it is possible to synthesize the area signal to the code data. According to this method, as shown in FIG. 7C, in a portion where a character region and a non-character character region coexist, the gradation quantization code φij has only one bit of information. Although it is slightly deteriorated, such a region is small in the entire image, and the deterioration is not so noticeable.
Further, since 2 bits of the information of La and Ld are used as the in-block area information bits, the image data at the time of decoding is affected, but the image quality is hardly noticeable.

[0030]

As is apparent from the above description, according to the first aspect of the present invention, it is not necessary to separately store and transmit the compressed data and the area determination signal.
It is possible to provide an image coding method capable of reducing the amount of memory without increasing the entire data amount and contributing to shortening of the transmission time of compressed data. This method also uses code information of an area other than the character area more frequently for embedding the area determination signal than the character area,
This is effective when seeking image quality with priority on the character area. According to the invention described in claim 2, similar to the invention described in claim 1,
Since it is not necessary to separately store and transmit the compressed data and the area determination signal, the total data amount does not increase, the memory amount can be reduced, and the transmission time of the compressed data can be reduced. An image coding method that can contribute can be provided. Further, the method according to claim 2 uses the code information of the character area more frequently for embedding the area determination signal than the area other than the character area, so that it is effective when obtaining the image quality with priority on the area other than the character area. is there.

According to the third aspect of the present invention, similarly to the first and second aspects of the present invention, the amount of memory can be reduced without increasing the entire data amount, and the transmission time of the compressed data can be reduced. Since it can contribute to shortening, etc., the code information of the character area and the code information of the area other than the character area are equally used for embedding the area determination signal, so either the image quality of the character area or the area other than the character area Can be provided when no priority is given to

According to the fourth aspect of the present invention, since it is not necessary to separately store and transmit the compressed data and the area determination signal, the total data amount does not increase,
The memory for storing the compressed data can be reduced in size,
It is possible to provide an image encoding device that can reduce the transmission time of compressed data. This apparatus also uses code information of an area other than the character area more frequently than the character area to embed the area determination signal, and is therefore effective when obtaining a character area priority image quality.

According to the fifth aspect of the present invention, similarly to the fourth aspect of the present invention, it is possible to reduce the size of the memory for storing the compressed data without increasing the total data amount, It is possible to provide an image encoding device capable of shortening the transmission time of an image. The device according to claim 5 also comprises:
Since the code information of the character area is used more frequently for embedding the area determination signal than the area other than the character area, it is effective when obtaining the image quality with priority on the area other than the character area.

According to the invention described in claim 6, similarly to the invention described in claim 4 or 5, the memory for storing the compressed data can be miniaturized without increasing the total data amount, It is possible to provide an image encoding device capable of shortening the transmission time of the compressed data, and to use the code information of the character region and the code information of the region other than the character region equally for embedding the region determination signal. It is possible to provide an effective image encoding device when one of the image qualities of regions other than the character region is not particularly prioritized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a digital copying machine according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an image storage unit in FIG. 1;

FIG. 3 is an explanatory diagram showing an example of storage of block area information bits.

FIG. 4 is an explanatory diagram showing a plurality of squares in a block.

FIG. 5 is an explanatory diagram showing another example of a plurality of squares in a block.

FIG. 6 is an explanatory diagram showing another example of storing block area information bits.

FIG. 7 is an explanatory diagram showing still another example of a plurality of squares in a block.

FIG. 8 is a block diagram showing a schematic configuration of an example of a conventional digital copying machine.

FIG. 9 is a block diagram illustrating a configuration of an image output unit in FIG. 8;

FIG. 10 is an explanatory diagram showing a relationship between a read gradation and a reproduced image.

FIG. 11 is an explanatory diagram showing a relationship between a read gradation and a reproduced image together with phase information.

FIG. 12 is an explanatory diagram showing the position of a phase determined by the arrangement of pixels.

FIG. 13 is a block diagram illustrating a configuration of an image processing unit in FIG. 8;

FIG. 14 is a plan view illustrating an example of a document to be read.

FIG. 15 is an explanatory diagram showing a relationship between an original image and a pixel block in the block coding method.

16 is a diagram showing an example of an algorithm of a compression by the block coding scheme.

[Explanation of symbols]

 1201 Scanner 1202 A / D converter 1203 Image processor 1204 Character area determination unit 1205 Gradation processor 1206 Image storage 1207, 1208 Signal switching unit 1209 Phase output unit 1210 Image output unit 1301 4-line FIFO unit 1302 Encoding unit 1303 Binary 4-line FIFO unit 1304 Area judgment signal synthesis unit 1305 Memory

Claims (6)

(57) [Claims] 1. A multi-tone pixel data forming image data is decomposed into a predetermined number to generate block data, and the density data of each of the decomposed block data is divided into two bits. To determine whether or not the image data is a character image, and to determine whether or not the image data is a character image, based on the determination result. A determination signal is output. When the area determination signal is a determination signal for a character area in the block data, 0 is set. When the block data includes a determination signal for a non-character area in the block data, 1 is set. If the block data includes a determination signal other than the character region in the least significant bit of one of the average data and the gradation width index, the region determination signal for each pixel is included in the lower bit of the gradation quantization code. Inserting an image encoding method, characterized in that. 2. Decomposing each of the multi-gradation pixel data forming the image data into a predetermined number to generate block data, and for each pixel of the decomposed block data, the density data is represented by 2 bits. To determine whether or not the image data is a character image, and to determine whether or not the image data is a character image, based on the determination result. A determination signal is output. If the area determination signal is a determination signal other than a character area in the block data, 0 is set. If the block data includes a character area determination signal in the block data, 1 is set. Inserting in the least significant bit of one of the average data and the gradation width index, if the block data includes a character region determination signal, an area determination signal for each pixel is placed in the lower bit of the gradation quantization code. To enter, image coding method, characterized in that. 3. A block data is generated by decomposing each of the multi-gradation pixel data forming the image data into a predetermined number, and the density data of each of the decomposed block data is represented by 2 bits. To determine whether or not the image data is a character image, and to determine whether or not the image data is a character image, based on the determination result. A determination signal is output. If the area determination signal is a determination signal for all character areas in the block data, a 2-bit signal 00 is output. Is a two-bit signal 1 when a character area and a non-character area determination signal are mixed in the block data.
1 is inserted into the lower two bits of one of the average data and the gradation width index of the compressed data or the least significant bit of both of the average data and the gradation width index, one bit at a time. Wherein, when a character area and a determination signal other than a character area coexist, an area determination signal for each pixel is inserted into lower bits of the gradation quantization code. 4. A data decomposing means for decomposing each of multi-tone pixel data forming image data into a predetermined number to generate block data, and a pixel of the block data decomposed by the data decomposing means. A data encoding unit for encoding the density data into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index every time; and determining whether the image data is a character image. An area determination data output means for outputting a binary area determination signal for each pixel based on the determination result of the image determination means; an area determination signal output by the area determination data output means Before the data encoding means outputs 0, when the determination signal of the character area is entirely included in the data, and 1 when the determination signal of the non-character area is included in the block data. In-block area determination bit insertion means for inserting into one of the least significant bits of the average data of the compressed data and the gradation width index, and when the block data includes a determination signal other than a character area, the gradation quantization code And a pixel unit area determination bit inserting unit for inserting an area determination signal for each pixel into lower bits of the image coding apparatus. 5. A data decomposing means for decomposing each of multi-tone pixel data forming image data into a predetermined number to generate block data, and a pixel of the block data decomposed by the data decomposing means. A data encoding unit for encoding the density data into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index every time; and determining whether the image data is a character image. An area determination data output means for outputting a binary area determination signal for each pixel based on the determination result of the image determination means; an area determination signal output by the area determination data output means Before the data encoding means outputs 0, when the data contains all the judgment signals other than the character area, and when the block data contains the judgment signal of the character area, 1 In-block area determination bit insertion means for inserting into the least significant bit of one of the average data and the gradation width index of the compressed data, and if the block data includes a determination signal of a character area, the gradation quantization code A pixel unit area determination bit insertion unit for inserting an area determination signal for each pixel into lower bits,
An image encoding device comprising: 6. A data decomposing means for decomposing each of multi-gradation pixel data forming image data into a predetermined number to generate block data, and a pixel of the block data decomposed by the data decomposing means. A data encoding unit for encoding the density data into compressed data including a 2-bit gradation quantization code, average data, and a gradation width index every time; and determining whether the image data is a character image. An area determination data output means for outputting a binary area determination signal for each pixel based on the determination result of the image determination means; an area determination signal output by the area determination data output means The 2-bit signal 00 is used for the determination signal of all character areas in the data, and the 2-bit signal 01 is used for the determination signal of all other than the character area in the block data. If the lock data includes a character area and a determination signal other than the character area, the two-bit signal 11 is converted to the lower two bits of one of the average data of the compressed data output by the data encoding means and the gradation width index, or An intra-block area determination bit insertion unit that inserts one bit at a time into the least significant bit of both the average data and the gradation width index, and a case where a character area and a non-character area determination signal are mixed in the block data. A pixel unit area determination bit inserting unit for inserting an area determination signal for each pixel into lower bits of the gradation quantization code.