JPH1098621A - Picture processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To comparatively and precisely evaluate an error and to execute efficient compression encoding in spite of the direction of correlation between blocks by dividing picture data into blocks, synthesizing the blocks in accordance with the representative values of the respective adjacent blocks and executing encoding. SOLUTION: An adaptive encoder 11 sequentially takes out block pictures from a block set buffer 10 collecting plural block pictures obtained by dividing original picture data and storing them and it encodes them. The adaptive encoder 11 sends the representative value of block picture data to a statistic computing element 13. The statistic computing element 13 obtains a difference between the representative value of the head block picture and the representative values of the successive block pictures and a selector 14 synthesizes the encoded block pictures whose representative values are considered to be the same through a code synthesizer 15. Thus, picture data where a blank or the part of the same color occupy much can be compressed/encoded with high efficiency by preserving minute information of picture data such as characters as they are.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital copying machine for reading an image of a document by a scanner, converting the image into digital image data, and temporarily storing the image data to record the image, and transmitting the image data. Facsimile, or an image processing device used for a personal computer or the like that performs communication and processing of image data, particularly an image suitable for compressing and encoding the informational redundancy of digital image data of a color still image The present invention relates to a processing device.

[0002]

2. Description of the Related Art Conventionally, various types of image processing apparatuses have been proposed as image processing apparatuses for compressing and encoding the informational redundancy of digital image data of this type. So-called block truncation coding (block truncation coding) in which data is divided into blocks including a predetermined number of pixels and coding is performed for each block.
coding (BTC) method.

[0003] Generally, in the BTC method in which coding is performed for each block, the coding is completed using information in one block, so that the correlation between the blocks is weakened, and the size of the block is increased in order to increase the coding efficiency. If you set it large,
The correlation between the blocks cannot be fully reflected in the code,
It was difficult to maintain the definition.

[0004] Therefore, as an encoding method capable of maintaining the definition while improving the encoding efficiency by utilizing the correlation between blocks, for example, a block truncation disclosed in Japanese Patent Application Laid-Open No. 57-127363 is disclosed. Encoding (DBTC)
A scheme has already been proposed.

In this DBTC coding method, when pixel values in a block are substantially uniform, the average pixel value of the block is used as the only pixel value information, and pixel information corresponding to the pixel indicating the average pixel value is assigned to all pixels. The pixel information is given by run-length (RL) encoding, and when the pixel value of the block of interest and the pixel value of the immediately preceding block are the same, the pixel information is encoded with a flag indicating that they are the same. The definition is maintained while considering the pixel values of the adjacent blocks while increasing the conversion efficiency.

In the block run length (BRL) coding system disclosed in Japanese Patent Application Laid-Open No. Sho 59-44175, coding efficiency is improved by performing run length (RL) coding of a block having specific pixel information. Is increasing.

Further, in the coding method disclosed in Japanese Patent Laid-Open No. 4-270473, a mode in which a block is approximated by one pixel value, and a plurality of blocks approximated by one pixel value are block-run-length (BRL). 2.) A mode for encoding, a mode for approximating a block with two pixel values, and a mode for approximating a block with four or more pixel values are provided to improve the encoding efficiency and image quality.

[0008] The Journal of the Institute of Image Electronics Engineers of Japan, Vol. 23, No. 1, 1994
In the coding method disclosed in “Image coding method based on segmentation and application to resolution conversion” on pages 3 to 10, the block is divided when the error between the original image and the code exceeds a predetermined value. In addition to maintaining the image quality, the regions having high correlation are integrated and chain-encoded after the division to secure the encoding efficiency.

[0009]

However, scanning by the block run length (BRL) disclosed in the above-mentioned JP-A-57-127363, JP-A-59-44175, and JP-A-4-270473. In the method that uses the correlation between blocks remaining in the direction, in a picture or the like having a strong correlation in the direction orthogonal to the scanning direction of the block, the correlation between the blocks cannot be reflected in the compression encoding, and the Is discontinuous, and the definition cannot be maintained.

The method in which the block size itself is not adaptively changed is relatively simple. For example, even when image data occupying a large amount of blank space or the same color portion is subjected to compression coding, the coding efficiency is reduced. There is a problem that it cannot be greatly improved.

Further, the Journal of the Institute of Image Electronics Engineers of Japan, Vol. 23, No. 1,
(1994) As disclosed in "Image coding scheme based on segmentation and application to resolution conversion" on pages 3 to 10, in the case of a scheme in which a block size is adaptively changed by dividing a block, The problem is the evaluation of the error value for determining whether the error between the original image and the code exceeds a predetermined value.

That is, when the block size is large, when the error value is evaluated, whether the error value is a value generated by noise dispersed throughout the block or a pattern actually existing in a limited place It is difficult to discriminate based on only the error value, whether it is a value generated by image data or the like. For this reason, there is a new problem that not only is it susceptible to the noise dispersed in the entire block, but also the reproducibility of an image such as a figure that actually exists locally is reduced.

In addition, when chain coding is performed by integrating block regions having high correlation, if the block size is set large, the code amount increases accordingly, so that a large improvement in coding efficiency cannot be expected. There is also a problem that.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide an image or the like having a strong correlation in a direction orthogonal to the block scanning direction. Image processing that can reflect the correlation between blocks in the compression encoding, is less susceptible to noise dispersed throughout the block, and maintains the definition while improving the encoding efficiency. It is to provide a device.

[0015]

According to a first aspect of the present invention, there is provided an image processing apparatus which divides input image data into blocks and encodes each block. A dividing unit that divides the input image data into blocks each including a predetermined number of pixels; a statistical information calculating unit that calculates statistical information of pixel data included in each of the blocks; and a statistical information obtained by the statistical information calculating unit. Determination means for determining whether each block is a first block to be encoded by integrating with a plurality of peripheral blocks or a second block to be encoded without being integrated based on Integrating means for integrating the first block and a plurality of blocks around the first block to generate an integrated block; and determining a representative value for the integrated block and the second block. A representative value calculating unit that, and having a coding means for coding for these representative values.

Further, in the configuration according to the second aspect,
2. The image processing apparatus according to claim 1, wherein the encoding unit applies one of a plurality of encoding methods based on the statistical information or a determination result of the determination unit. .

Further, in the configuration according to the third aspect,
3. An image processing apparatus according to claim 2, wherein said integrating means integrates a plurality of blocks into one or a plurality of predetermined shapes, or integrates a predetermined number of blocks.

Further, in the configuration according to the fourth aspect,
4. The image processing apparatus according to claim 3, wherein the encoding unit includes a first encoding unit that represents a block by one representative value, and a first encoding unit that represents the block by one representative value obtained from a predetermined reference block. 2 encoding means.

(Operation) According to the image processing apparatus of the present invention, error values can be evaluated relatively accurately by integrating and encoding blocks according to the representative value of each adjacent block. Thus, efficient compression encoding can be performed regardless of the direction of correlation between blocks.

In other words, the image processing apparatus according to the present invention changes the block size according to the pixel information of the local area, and encodes the blocks in units convenient for improving the encoding efficiency.

Further, by setting the shape of the integrated block to a predetermined shape, the shape and size of the block can be clearly indicated only by adding a tag. The amount can be reduced.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an image processing apparatus according to the present invention. Reference numeral 1 denotes original image data of a document read and input by a scanner or the like (not shown); m pixels, n pixels in the horizontal direction (for example, m × n = 8 × 8 = 6
The block 3 divided into a predetermined size (4 pixels) is a block set in which the blocks 2 divided into the predetermined size are grouped by x blocks in the vertical and horizontal directions.

Reference numeral 4 denotes a buffer for temporarily storing image data 2 divided into blocks to be coded, 5 a representative value calculator for calculating one representative value representing one block, and B
The encoding means includes an encoder that employs one or a plurality of encoding schemes such as the TC and DCT encoding schemes.

Reference numeral 6 denotes a statistic calculation means for comparing the original image data 1 with a decoded image of the code obtained by the coding means 5 to calculate a predetermined statistic. A selection unit 8 for selecting whether or not to integrate blocks based on the obtained statistics, and a storage / transmission unit 8 for storing and transmitting the image data encoded by the encoding unit 5.

FIG. 2 is a more specific hardware block diagram of the image processing apparatus according to the embodiment of the present invention configured as described above.

In the drawing, reference numeral 9 denotes original image data 1 for one page of a document read by a scanner (not shown).
Is a block set image buffer for temporarily storing image data 2 for one block set (for example, m × n = 8 × 8 = 64 pixels).

Numeral 11 adaptively encodes image data 2 corresponding to a set of blocks into data obtained by converting the image data 2 into one or more kinds of corresponding codes such as BTC or DCT coding in units of one block. An adaptive encoder 12 is an intermediate code buffer for temporarily storing codes for one block set encoded by the adaptive encoder 11.

Reference numeral 13 denotes a statistic calculator which compares one or more types of encoded image data obtained from the adaptive encoder 11 with the original image data 2 to generate a predetermined statistic. Calculate. A selector 14 for outputting one or more types of encoded image data obtained from the adaptive encoder 11 based on the statistics obtained from the statistics calculator 13 as it is; Select whether to combine and output.

Reference numeral 15 denotes a code integrator for integrating the codes obtained from the adaptive encoder 11. Reference numeral 16 denotes a synthesizer that synthesizes the code output from the adaptive encoder 11 as it is and the code integrated by the code integrator 15. Reference numeral 17 denotes an intermediate code buffer, which temporarily stores the code obtained from the synthesizer 16.

Numeral 18 denotes a selector, which is a statistic calculator 1
Based on the statistic obtained from No. 3, it is selected whether the code obtained from the synthesizer 16 is output as it is or the code is converted and output. Reference numeral 19 denotes a code converter.
The code is converted when the conversion and output of the code are selected by 8.

Reference numeral 20 denotes a synthesizer for synthesizing the code output from the synthesizer 16 as it is and the code converted by the code converter 19. A block set code buffer 21 temporarily stores codes for one block set. Reference numeral 22 denotes a frame code buffer, which stores encoded image data for one page.

In the present embodiment, the shapes of the blocks to be integrated are set so as to be only similar to the shape of the first divided block 2.

Next, the operation of the image processing apparatus according to the embodiment of the present invention shown in FIG. 2 will be described with reference to the encoding flowchart of FIG.

First, in the image processing apparatus, one page of original image data 1 of a document read by a scanner (not shown) is taken into the frame image buffer 9 and stored. Next, in order to encode the original image data 1 stored in the frame image buffer 9 for each block, as shown in FIG. The pixel data 2 for one block of 64 pixels is divided, and the pixel data 2 for the divided one block or the pixel data 2 obtained by grouping the pixel data 2 for the divided one block into a plurality of blocks is used. It is taken in and stored in the block set image buffer 10 (step 1).

As described above, when the original image data 1 for one page of the original is divided into pixel data 2 for one block, the total number of pixels in the vertical and horizontal directions of the original image data 1 for one page of the original Is not divisible by the number of vertical and horizontal pixels corresponding to one block, that is, if the last number of pixels in the vertical and horizontal directions is less than a predetermined m or n (for example, m = n = 8), FIG. As shown in FIG. 5, a pixel having a predetermined pixel value is added to the last pixel in the vertical and horizontal directions, or the last pixel in the vertical or horizontal direction of the original image data 1 is copied by a predetermined number, By filling the pixel data 2 of the last block in the vertical direction and the horizontal direction, the original image data 1 for one page is completely divided into an integral number of blocks.

Next, a predetermined block (for example, 8 × 8)
= 64 pixels) from the block group image buffer 10, and the adaptive encoder 1
1 (step 2), and the process is repeated until the encoding of all pixel data 3 for one block set is completed (step 3). Now, assuming that pixel data 2 of 8 × 8 = 64 pixels is one block, as shown in FIG. 6, for example, a set of four blocks in a vertical direction and a horizontal direction becomes a block set 3. However, this one block set 3 is not limited to a set of four blocks 2 in the vertical direction and the horizontal direction, but an arbitrary number x such as two or eight in the vertical and horizontal directions. Needless to say, it is also possible to use a set of only these.

The adaptive encoder 11 includes an encoder that represents the pixel data 2 for one block by one representative value, for example, the average value of the pixel values in the block. The encoder 11 having the best SN ratio is adaptively selected based on the statistic obtained by S13, for example, the SN ratio. The selected encoder 11 is described together with the block size by the tag at the head of the code of each block.

To further explain, for example, when an average value of m × n pieces of pixel data of one block is used as a representative value for representing the pixel data 2 of one block, Average value p ₀ of pixel data 2
Is given by p ₀ = Σa _ij / (m × n), where a _ij is the density of each pixel in the block.

Next, as shown in FIG. 6, for example, a Hilbert scan or the like is used to maintain the correlation between the codes of one block set and the adjacent pixels as much as possible. Are arranged one-dimensionally (step 4). In order from the beginning of the code, whether all four consecutive codes are codes representing one block corresponding to one pixel value or whether the information described in the tag is Based on
The determination is made by the selector 14 (step 5).

If the four consecutive codes are codes representing one block with one representative value, FIG.
As shown in the figure, the statistical value calculator 13 determines the difference between the representative value of the first block and the representative values of the other three blocks to determine whether or not the representative values of four consecutive blocks can be regarded as the same. If the four blocks can be regarded as the same (if the difference between the maximum value and the minimum value of the representative values of these blocks is equal to or less than a predetermined value), as shown in FIG. And the four codes are converted into a code integrator 1
5, a code representing a block having a similar shape twice as long and wide as the original block is generated by the synthesizer 16 (step 7).

Thereafter, the above steps 5 to 7
Is a code that represents one block of pixel data by one pixel value, and determines whether the reference block, for example, the pixel value obtained from the immediately preceding block, can be regarded as the same as the pixel value obtained from the reference block. The difference from the value is obtained by the statistic calculator 13 and determined by the selector 18 (step 8).

At this time, the reference block does not need to be a code representing one block of pixel data by one pixel value. For example, even if the code has two pixel values, it may be determined that the average value of one or both of them is used as the representative value of the block.

When the selector 18 determines that a block is a code representing one pixel value and can be regarded as the same as the pixel value obtained from the reference block,
As shown in FIG. 7, using a coder that converts a code by a code converter 19 to represent a block with one pixel value obtained from a predetermined reference block and using only a tag indicating a block size, The information is omitted (step 9). Further, the code converted by the code converter 19 and the code output from the combiner 16 are combined by the combiner 2
0 and the block set code buffer 21
Is stored.

Then, the above steps 5 to 9
Are repeated until all blocks of one block set are completed (steps 10 and 11).

(Modification) In the above embodiment, the case where the image processing apparatus is constituted by hardware including an encoder and a selector has been described. However, the present invention is not limited to this. Of course, it may be configured.

In the above embodiment, when the correlation between adjacent blocks is high, the processing from step 5 to step 9 is performed recursively, and the processing is repeated until the block size reaches a predetermined size. You may.

Further, in the above-described embodiment, a configuration may be adopted in which a code obtained after a series of processes is subjected to lossless compression encoding.

[0048]

As described above, in the image processing apparatus according to the present invention, relatively simple image data, such as a document for business communication, occupied mostly by blanks or the same color portion, and detailed information of the image data such as characters can be obtained. It is possible to perform compression encoding with extremely high efficiency while preserving the data.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of an image processing apparatus according to the present invention.

FIG. 2 is a hardware block diagram illustrating a more specific configuration of the image processing apparatus according to the embodiment.

FIG. 3 is a flowchart illustrating an operation of the image processing apparatus according to the embodiment.

FIG. 4 is an explanatory diagram showing one block.

FIG. 5 is an explanatory diagram showing a state in which one page of original image data is divided.

FIG. 6 is an explanatory diagram showing an encoding state of a block set.

FIG. 7 is an explanatory diagram showing an encoding state of a block set.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Original image data 2 Divided block 3 Block set 4 Buffer 5 Encoding means 6 Statistics calculation means 7 Selection means 8 Storage / transmission means

Claims (4)

[Claims] 1. An image processing apparatus that divides input image data into blocks and encodes the blocks, and divides the input image data into blocks including a predetermined number of pixels. Statistical information calculating means for calculating statistical information of pixel data included in each block; and, based on the statistical information obtained by the statistical information calculating means, each block is integrated with a plurality of peripheral blocks to perform coding. Determining means for determining whether the block is a first block or a second block to be encoded without being integrated; integrating the first block with a plurality of peripheral blocks; Integrating means for generating; representative value calculating means for obtaining a representative value for the integrated block and the second block; encoding means for performing coding on these representative values An image processing apparatus comprising: 2. The coding apparatus according to claim 1, wherein the coding unit applies one of a plurality of coding methods based on the statistical information or a determination result of the determination unit. Image processing device. 3. The image processing apparatus according to claim 2, wherein the integration unit integrates a plurality of blocks into one or a plurality of types of predetermined shapes, or integrates a predetermined number of blocks. 4. The encoding means comprises: first encoding means for representing a block by one representative value; and second encoding means for representing the block by one representative value obtained from a predetermined reference block. The image processing apparatus according to claim 3, comprising: