JP3134584B2 - Image data processing apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for compressing and storing information of a halftone image, and more particularly to a technique for always compressing a halftone image at a constant compression ratio.

[0002]

2. Description of the Related Art When displaying or printing a halftone image, the density of the image must be stored in a storage medium in advance. For example, in order to be able to express 256 gray levels in a monochrome image, a storage device of 8 bits per pixel is required. Further, if the image is color, the required storage capacity can be further increased by a factor of three or four.
(Since they must correspond to RGB or YMCB colors, respectively). As described above, an image data storage device that captures, stores, and outputs image data to a display device or a printing device requires an extremely large amount of storage media.

[0003] To efficiently store such a large amount of information, compression methods such as DPCM and JPEG have been proposed.

[0004] However, since these methods are the compression ratio according to the type of the record information to be place a compression would change, and the disadvantage that can not be predicted or in advance how much compression is applied, the cut-and-paste Even if it is attempted to use graphic information that can be used, there is a drawback that it is impossible to instantaneously determine at which position on the recording medium the information to be processed exists, so that it is impossible.

[0005] Therefore, to predict whether advance how much compression is applied, leaving the compression method of constant compression rate to what position in can be determined instantly on information storage unit to be processed for the idea Was done.

Among them, Mitsubishi Electric's “Fixed GBTC Algorith”
m ″ divides image data into blocks of 4 × 4 pixels, and divides 16 pixels included in each block into 4 blocks.
The data is classified into stages, and these values, the average value of the density data of one block, and the dynamic range are stored to compress and store. As a result, if one pixel has an information amount of 1 byte in the original image, 16 bytes are required for one block, but 6 bytes are required for 2 bits × 16 pixels + 1 byte + 1 byte.

[0007]

However, on the other hand, in the above method, on the principle that the original density data is reproduced from the average value and the dynamic range of the density data, it is sufficient that the distribution of the density data is close to the normal distribution. However, if the distribution is far from the normal distribution, there is a disadvantage that the reproduced image is greatly different from the original image.
Moreover, the kind of image data which particularly requires compression usually shows a distribution far from the normal distribution.

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a drawback, and an object of the present invention is to store image data representing halftone density of continuously transmitted pixels and then display the image data. In an image data storage device to be output to a device or a printing device, it is possible to compress the image data at a constant compression ratio, and thereafter, the reproduced image obtained by outputting the image data can be seen as close as possible to the original image Is to do so.

[0009]

In order to solve such a problem, an image data storage device according to the present invention converts the image data contained in each image processing unit divided by N × N pixels from 1 to 1 according to the value. Classifying means for classifying into K stages; and N × N based on the classification result of the classifying means.
An image processing unit storing means for replacing each image data of a pixel image processing unit with stage data of 1 to K and storing the image data in each stage of 1 to K; Representative value determining means for determining a value, the representative value determined by the representative value determining means,
A step representative value storage unit for storing in order of steps from 1 to K, and a corresponding representative value from the step representative value storage unit according to each step data stored in the image processing unit storage unit. And representative value output means for extracting the value and outputting the value as image data at the time of an output command.

[0010]

FIG. 1 is a diagram showing a basic configuration of the present invention.
In FIG. 1, input image data 1 is first sent from a host computer or the like to the present image data storage device. The input image data 1 here is, for example, data expressing the density gradation of a plurality of pixels constituting a certain image, and here is composed of 8 bits. This allows
It is possible to express a density gradation from 0 to 255.

[0011] Input image data 1 sent continuously
Is first divided into image processing units of 4 × 4 pixels, and processing is performed based on this unit.

Next, in this image processing unit, the input image data 1 is divided into four stages based on the classification means 2. By dividing into four stages, 8-bit information represented by 0 to 255 is converted into 2-bit information represented by 1 to 4. This time, the following method (1) was adopted as the classification method, but other methods such as (2) and (3) are also possible.

(1) Equivalent classification; 0 to 63, 64 to 1
27, 128 to 191 and 192 to 255.

(2) Both-end emphasis classification; 0 to 42, 43
, 127 to 128, and 213 to 255, the width of both ends is 1, and the middle two are divided into 2 widths.

(3) Central part emphasis classification; for example, 0 to 8
3, 84 to 127, 128 to 171, 172 to 2
A method in which the two widths on the middle side are set to 1 and the widths at both ends are set to 2, for example, 55.

The image data of each pixel converted into the 2-bit information represented by the 1- to 4-stage data is stored by the image processing unit storage means 3.

On the other hand, in each of the stages from 1 to K, the representative value determining means 4 performs a process of determining a representative value from the image data group included in each stage. There are various methods for determining the representative value, but the following is the most basic.

(1) A method of taking an average value of all density data of a target stage.

(2) A method of obtaining the median value of all density data of the target stage.

(3) A method of taking the most frequently occurring value of all density data at the target stage.

In the present embodiment, the method of taking the average value of (1) is adopted, and this value is written in the step representative value storage means 5 as a representative value.

As described above, data can be stored at a constant compression rate.

At the time of output, output image data 7 is created based on the data stored in the image processing unit storage means 3 and the step representative value storage means 5, and this data is output. In this process, a corresponding representative value is extracted from the step representative value storage means 5 according to each step data stored in the image processing unit storage means 3, and this value is output as output image data 7. For example, a certain pixel of a certain image processing unit has 172 as input image data 1, and this is 3
And the stage representative value storage means 5
If it is determined that the representative value of the stage data is 165, the output is 165.

The above processing will be described more specifically with reference to FIG.

The image data for each pixel is from 0 to 2
Input image data 1 sent as an integer value within the range of 55 is divided into 4 × 4 image processing units 22 (a). In each image processing unit, the image data is 1,
It is classified into 2, 3, and 4 stage data 23 (b). In each of the four stages, an average value is calculated from each of the four pieces of input image data 1 belonging thereto, and a stage representative value storage unit 5 is created (c). At the same time, the image processing unit is filled with the stage data of 1 to 4, and the image processing unit storage unit 3
1 (d). At the time of output, the representative value output means stores the step representative value storage means 5 and the image processing unit storage means 3.
, A 4 × 4 image processing unit for output is created, and this is transferred to the output device.

Now, the image to be processed is 40 pixels × 4
Consider a storage capacity required for storing information in the case of being composed of 0 pixels. The target image is divided into 100 image processing units, and 16
Since there are pixels and 2 bits are required for each pixel, 2 bits × 16 × 100 = 3200 bits = 400 bytes. On the other hand, the storage capacity required for the step representative value storage means 5 requires 8 bits (1 byte) for one of the representative values in the range of 0 to 255,
Since there are four stages, four bytes are required, so that 4 bytes × 100 = 40 bytes. Therefore, according to the present invention, 400 bytes + 400 bytes = 800 bytes. However, according to the conventional method, one byte is required for one pixel, and since there are 1600 pixels, 1 byte × 160 = 1600 bytes. After all,
It can be seen that the storage capacity required to store the image information according to the present invention is half that of the conventional method. This compression ratio is 1
No matter how many pixels each image is composed of, the compression ratio is always constant. Of course.

As described above, according to the present invention, it is possible to store the image information transmitted as the density data of 0 to 255 with a smaller capacity as compared with the case where the image information is stored without any processing. Become. In this case, the output image is different from the original image because a representative value of each of the divided stages is output instead of the original density data.
However, by finely dividing the steps according to the degree of variation in the density data of the original image, and accurately taking representative values at each step, the output image can be faithfully reproduced to the original image so that it cannot be distinguished by the human naked eye It is possible.

[0028]

The image data storage device according to the present invention has N × N
A classifying unit 2 for classifying input image data 1 included in each image processing unit 22 separated by pixels into stages from 1 to K according to the value thereof, and the N × N based on the classification result of the classifying unit 2 An image processing unit storing means 3 for storing each input image data 1 of the pixel image processing unit 22 by replacing the input image data 1 with stage data of 1 to K, and an image included in each stage in each of the stages 1 to K A representative value determining means for determining a representative value from a data group; a step representative value storing means for storing the representative values determined by the representative value determining means in the order of 1 to K; A representative value corresponding to each step data stored in the processing unit storage means 3 is extracted from the step representative value storage means 5 and this value is output as image data at the time of an output command. output By having a stage 6, it is possible to store the images at a fixed compression ratio.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a basic configuration of the present invention.

FIG. 2 is a diagram illustrating the present invention using specific numerical values.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input image data 2 Classification means 3 Image processing unit storage means 4 Representative value determination means 5 Step representative value storage means 6 Representative value output means 7 Output image data

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/41-1/419 G06T 9/00

Claims (4)

(57) [Claims] 1. An image data processing device for converting and storing image data of each pixel representing a halftone density, wherein image data contained in each image processing unit divided by N × N pixels is converted from 1 to 1 according to its value. Classifying means for classifying into K (K is a natural number smaller than N × N); based on the classification result of the classifying means, individual image data included in the image processing unit is classified into the 1 Image processing unit storage means for replacing and storing step data corresponding to the steps from (k) to (k); and, for each of the steps (1) to (K), representative value determining means for determining a representative value from an image data group included in the step. A step representative value storage unit that stores the representative value determined by the representative value determination unit for each of the step data corresponding to steps from 1 to K; A representative value output unit that replaces each stored stage data with a corresponding representative value based on the stage representative value storage unit and outputs the corresponding representative value. 2. The image data processing apparatus according to claim 1, wherein said K is equal to N. 3. The image data processing apparatus according to claim 1, wherein said K and N are both 4. 4. An image data processing method for converting and storing image data of each pixel representing a halftone density, wherein the image data included in each image processing unit divided by N × N pixels is converted into an image data. A classifying step of classifying the image data into stages of 1 to K (K is a natural number smaller than N × N) according to the value; and a process of classifying individual image data included in the image processing unit from the stage of 1 to K to which the own pixel belongs. An image processing unit storing step of replacing the stored data with the step data to be stored; a representative value determining step of determining a representative value from the image data group included in each of the steps 1 to K; And a step of storing a representative value for each of the step data corresponding to the steps from (k) to (k). At the time of outputting the image data, each stored step data is replaced with a corresponding representative value. And outputting a representative value.