JPH06253153A - Picture coding/decoding device - Google Patents

Abstract

PURPOSE:To reduce data quantity of compressed picture data more. CONSTITUTION:The device is provided with a picture conversion section 12 converging multi-gradation picture data represented in n-bits (n>=2, n is an integer) per one picture element into converted picture data in which the change in each bit is less between adjacent picture elements is less, a picture separation section 14 separating the obtained converted picture data into binary picture data by n-planes for each bit, a binary picture coding section 18 coding the binary picture data by the n-planes respectively to generate code picture data, a binary picture decoding section 22 decoding the code picture data obtained by the binary picture coding section 18 to generate binary picture data by n-planes, a picture synthesis section 26 synthesizing conversion picture data from the binary picture data by n-planes generated by the binary picture decoding section 22, and a picture reproduction section 28 reproducing multi-gradation picture data from the picture data synthesized by the picture synthesis section 26.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the encoding of multi-tone images.
The present invention relates to an image encoding / decoding device that performs decoding.

[0002]

2. Description of the Related Art The following method is one of the encoding methods for a multi-gradation image in which one pixel has n bits.

First, 1 is set for each bit of multi-tone image data.
One image is taken out as one image. Since the image for one screen is a binary image, one original multi-tone image data becomes binary image data for n planes.

Next, each binary image is converted into a binary image coding method (MH (Modified Huffman)) based on run length compression.
Method, MR (Modified READ) method, etc.). As a result, compressed image data for n planes can be created. An image encoded by such a method can be decoded by the following procedure.

First, the compressed image data for n planes is decoded to generate binary image data for n planes. next,
The pixel data of each binary image for n planes are combined into multi-tone image data of n bits for each pixel. As described above, in the conventional image encoding / decoding device, the encoding / decoding of the multi-tone image data can be performed by using the method described above.

[0006]

By the way, in the binary image coding system based on run-length compression, basically two
The smaller the change from 0 to 1 or 1 to 0 in the adjacent dots in the value image, the smaller the data amount of the compressed image data can be.

However, if the above-mentioned method is directly applied to each bit of the normal multi-tone image data, the compressed image data does not become so small. This is because the bit pattern of each pixel data of the multi-tone image data changes. Ordinary multi-gradation image data is a numerical value (hereinafter,
The one represented by the gradation value) is used as it is.

Therefore, as shown in FIG. 6, a plurality of bits may change according to the change of the gradation value. For example, in an image in which a large number of pixels having gradation values 7 and 8 are adjacent to each other as shown in FIG. 7, all 4 bits change between the pixels. FIG. 8 shows an image (binary image 1 to 4) for each bit of the multi-tone image data shown in FIG.
It is represented by. FIG. 8A shows the first bit, and FIG.
8B is the second bit, FIG. 8C is the third bit, and FIG.
(D) represents the binary image by the 4th bit, respectively. As shown in FIG. 8, at pixel positions where pixels having gradation values 7 and 8 are adjacent to each other, 1 is set in all of the binary images 1 ′ to 4 ′.
And 0 are adjacent.

That is, when the image is decomposed into binary images bit by bit, all binary images frequently repeat the change of 0 and 1. Therefore, in the binary image encoding system based on run-length compression, the amount of compressed image data cannot be made sufficiently small. The changing number of bits in FIG. 6 is usually called the Hamming distance. For example, if 2 bits change, the Hamming distance becomes 2.

The present invention has been made in view of the above points, and an object of the present invention is to provide an image coding / decoding device capable of reducing the data amount of compressed image data.

[0011]

According to the present invention, multi-tone image data represented by n bits per pixel (n ≧ 2, n is an integer) has little change in the value of each bit between adjacent pixels. Image conversion means for converting such converted image data, image separation means for separating the converted image data obtained by the image conversion means into binary image data for n planes for each bit, and the image separation. N obtained by means
Binary image coding means for respectively coding the binary image data of the planes to generate coded image data, and the coded image data obtained by the binary image coding means are decoded to obtain n planes. Binary image decoding means for generating binary image data, and n generated by the binary image decoding means.
An image synthesizing unit for synthesizing the converted image data from the binary image data of the plane and an image reproducing unit for reproducing the multi-tone image data from the converted image data synthesized by the image synthesizing unit are provided. To do.

[0012]

According to this structure, multi-tone image data in which each pixel is represented by n bits is encoded as one binary image data for each bit. At that time, the bit pattern of each pixel of the multi-tone image data is converted into a predetermined conversion image data set in advance. Since the converted image data is set so that the change in the value of each bit between adjacent pixels is small, the change in the bit between adjacent pixels in the binary image data is small. Therefore, encoding of binary image data can be efficiently executed, and the data amount of the entire encoded data can be reduced.

[0013]

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 the configuration of an image encoding / decoding device according to an embodiment of the present invention. As shown in FIG. 1, the image encoding / decoding device includes an image converting unit 12, an image separating unit 14, a selecting unit 16, a binary image encoding unit 18, a storage unit 20, a binary image decoding unit 22, and a selecting unit. 24, an image synthesizing unit 26, and an image reproducing unit 28.

As shown in FIG. 1, the image encoding / decoding apparatus receives an image conversion unit 12, an image separation unit 14, and a selection unit 1 for multi-tone image data input from an image input device 10.
6, and the binary image encoding unit 18 constitutes an encoding system. In addition, the binary image decoding unit 22, the selection unit 24,
A decoding system is configured by the image composition unit 26 and the image reproduction unit 28, and an image corresponding to the decoded multi-tone image data is displayed on the image display device 30. The image input device 10 inputs multi-tone image data represented by n bits for each pixel, which is a processing target in the image encoding / decoding device.

The image conversion unit 12 converts the multi-tone image data input from the image input device 10 into converted image data having a bit pattern of the same number of bits corresponding to the bit pattern of n bits for each pixel. It is to convert. The image conversion unit 12 has a conversion table as described later.

The image separation unit 14 forms the converted image data represented by n bits per pixel into one screen for each of the first, second, ..., Nth bits, and converts it into binary image data for n planes. To separate. The selection unit 16 has two parts for n surfaces.
The binary image data to be encoded is selected from the value image data.

The binary image coding unit 18 sequentially codes the binary image data selected by the selection unit 16 by a binary image coding system based on run length compression,
The compressed image data for n planes is generated. The storage unit 20 is for accumulating compressed image data for n planes. The compressed image data stored in the storage unit 20 is supplied to the decoding system. The binary image decoding unit 22 includes the storage unit 2
The binary image data for n planes stored in 0 is decoded to reproduce the binary image data.

The selection unit 24 sequentially selects one binary image data from the binary image data for n surfaces obtained by the binary image decoding unit 22 and outputs the data of a predetermined pixel. is there. The image synthesizing unit 26 synthesizes the converted image data represented by n bits for each pixel from the binary image data for n planes.

The image reproducing unit 28 converts the converted image data synthesized by the image synthesizing unit 26 into corresponding multi-tone image data for each pixel to reproduce the original multi-tone image. is there. The image display device 30 displays the multi-tone image data reproduced by the image reproduction unit 28.

Next, the operation of this embodiment will be described.
Here, multi-tone image data represented by 4 bits (16 tones) per pixel will be described as an example. In the present embodiment, with respect to continuous tone values, the bit pattern is converted into converted image data in which only 1 bit changes and the other 3 bits do not change, and encoding / decoding is performed using this converted image data. It is to convert. That is, gradation values 7 and 8
Even between pixels, the change in bit pattern is only 1 bit.

First, the operation of the coding system of the image coding / decoding apparatus will be described. FIG. 2 is a diagram for explaining the operation of the coding system. First, the image input device generates the multi-tone image data 40 of one screen and supplies it to the image encoding / decoding device. The image conversion unit 12 converts the multi-tone image data 41 of each pixel into converted image data 42.

The image conversion unit 12 converts the bit pattern of each gradation value into a predetermined bit pattern (value of converted image data) according to the conversion table as shown in FIG. For example, the bit pattern of the multi-tone image data “0111” is converted into the converted image data “0100”. As shown in FIG. 3, the number of changing bits is 1 bit for all continuous gradation values.

The image separating section 14 separates the converted image data for each pixel to obtain binary image data for each bit. Therefore, binary image data 43 to 46 for four screens are generated. For example, by performing the above-described processing on the multi-tone image data shown in FIG. 7, binary image data for four screens as shown in FIG. 4 can be obtained. 2A shows a binary image with the first bit, FIG. 2B shows the second bit, FIG. 2C shows the third bit, and FIG. 2D shows the fourth image with the fourth bit. As can be seen by comparing with FIG. 8, there is less change between adjacent pixels. In particular, FIG.
In (b) and (c), there is no bit change.

The selection unit 16 uses the binary image data 43 to 46.
Are sequentially selected and output to the binary image encoding unit 18. The binary image encoding unit 18 encodes the binary image data 43 to 46 using a binary image encoding method based on runless compression and compresses the four screens of compressed image data 47 to 47.
Generate 50. The compressed image data 47 to 50 are stored in the storage device 20. This compressed image data 47-50
4 is obtained by encoding binary image data with little change between adjacent bits, as shown in FIG. 4, and therefore has a smaller amount of data than in the case of binary image data shown in FIG. Has become.

Next, the operation of the decoding system of the image coding / decoding apparatus will be described. FIG. 5 is a diagram for explaining the operation of the decoding system. First, the binary image decoding unit 22 decodes the compressed image data 47 to 50 for four screens stored in the storage device 20 for each screen to generate binary image data 51 to 54. This is the same as the binary image data 43 to 46, respectively.

The selecting section 24 sequentially selects the binary image data 51 to 54 for each pixel and outputs it to the image synthesizing section 26 (data for 4 bits). The image composition unit 26 includes a selection unit 24.
The converted image data 55 is generated by using the 4-bit data from 1 to 1 as the data for one pixel.

The image reproducing unit 28 converts the converted image data 55 synthesized by the image synthesizing unit 26 into each pixel as shown in FIG.
Depending on the relationship between the converted image data value and the gradation value shown in
The original multi-tone image data 5 converted to multi-tone image data
6 is reproduced. The multi-tone image data 56 is the same as the multi-tone image data 40 before encoding. The image display device 57 displays the decoded image based on the reproduced multi-tone image data 56.

In this way, after converting multi-tone image data in which one pixel is represented by a plurality of (n) -bit data into converted image data in which the number of bits changing between successive tone values is reduced. , Each of the bits (first, second, ..., Nth) are separated and encoded as binary image data for n planes. Therefore, in each binary image data, the value switching (0 or 1) between adjacent pixels is reduced, and the overall compression rate is improved.

In the case where the compressed image data is stored in the storage device 20 as in the present embodiment, the amount of the compressed image data becomes small, so that the compressed image data is stored in the storage device 20. There is also an effect that the time for transferring to the value image decoding unit 22 is shortened, and as a result, the display on the image display device 30 becomes faster.

In the above-described embodiment, as shown in FIG. 3, conversion image data is converted so that the number of bits changing between continuous gradation values is reduced. The value of the converted image data corresponding to the image data of each gradation value may be determined based on the distribution of gradation changes between existing adjacent pixels. Further, the multi-tone image data of 4 bits for each pixel has been described as an example, but the tone value is not particularly limited.

[0031]

As described above, according to the present invention, when multi-tone image data is separated into binary image data for a plurality of screens, it is converted into converted image data in which a change between adjacent pixels is small. Since the encoding is performed later, the compressed image data can be made smaller.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an image encoding / decoding device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the encoding system shown in FIG.

FIG. 3 is a diagram showing the contents of a conversion table referenced in this embodiment.

FIG. 4 is a diagram showing an example of a plurality of binary image data obtained by separating converted image data in this embodiment.

5 is a diagram for explaining the operation of the decoding system shown in FIG.

FIG. 6 is a diagram for explaining the value of each multi-tone image data of continuous tone values and the number of changing bits.

FIG. 7 is a diagram showing an example of a multi-tone image.

8 is a diagram showing an example of a plurality of binary image data obtained by separating the multi-tone image data shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Image input device, 12 ... Image conversion part, 14 ... Image separation part, 16, 24 ... Selection part, 18 ... Binary image coding part,
20 ... Storage unit, 22 ... Binary image decoding unit, 26 ... Image combining unit, 28 ... Image reproducing unit, 30 ... Image display device.

Claims (1)

[Claims] 1. Multi-gradation image data represented by n bits per pixel (n ≧ 2, n is an integer) is converted into conversion image data in which a change in bit value between adjacent pixels is small. Image conversion means for converting the converted image data obtained by the image conversion means,
An image separation unit that separates binary image data for n planes for each bit and a binary image that encodes the binary image data for n planes obtained by the image separation unit. Image coding means and coded image data obtained by the binary image coding means are decoded to generate binary image data for n planes. 2
A value image decoding means, and 2 for n planes generated by the binary image decoding means
An image code comprising: an image synthesizing unit for synthesizing the converted image data from the value image data; and an image reproducing unit for reproducing multi-tone image data from the converted image data synthesized by the image synthesizing unit. Decoding device.