JPH07226848A - Picture signal encoding device - Google Patents

Abstract

PURPOSE:To provide a picture signal encoding device which can edit picture data through the use of a buffer memory with small capacity and whose compression efficiency of picture data is high. CONSTITUTION:A picture is inputted from a picture input device 201, a data comprssion processing is conducted, and the picture is preserved in a storage medium. The picture which is compression-preserved is data-expanded at need, and the picture is outputted from a picture output device 203. In the picture signal encoding device of such constitution, a fixed length compression/expansion circuit 204 conducts a fixed length compression/processing, and data is written into a buffer memory 205, then a variable length compression/expansion circuit 206 conducts a variable length compression processing and data are stored in the storage medium 208 of a hard disk or the like through a buffer memory 207.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal coding apparatus having a high-efficiency coding apparatus for a digital signal of a still image, which is applied to a digital color copying machine, an electronic filing apparatus, a facsimile and the like.

[0002]

2. Description of the Related Art When digital image data is stored in a storage medium such as a hard disk, the required storage capacity is (number of pixels x gradation) bits, which is enormous for storing high resolution and full color images. A storage medium with a large capacity was required. Further, in order to transmit an enormous amount of data, it takes a long time to transmit the data.

In order to improve this, it has been conventionally attempted to reduce the amount of transmission and increase the storage efficiency of a storage medium by compressing data. At the same time, however, it is also important to maintain and improve the image quality of the input image data, which is a requirement that is contrary to the improvement of compression efficiency that reduces the data amount. In order to satisfy these requirements at the same time, conventionally, variable length compression is mainly used in data compression.

FIG. 3 is a schematic block diagram of an image signal encoding device having an image input device, an image output device and an image storage device according to the prior art.

Image data input from the image input device 101 is input to a variable length compression circuit 103 via an image quality correction device 102 that improves the image quality by correcting the characteristics of the input device with a filter or the like. The image data compressed here is once output to the buffer memory 105, and is written to the storage medium 106 such as a hard disk when the compression processing is completed. When reading the stored image, the above procedure is reversed and the image is output from the image output device 103.

The reason why the compressed data is temporarily stored in the buffer memory 105 is that the data is written in the storage medium 106 at a high speed and in a batch, the processing time is shortened, and the speed of the entire system is increased.

Since the apparatus according to the prior art uses variable length compression for compression, there is almost no deterioration in image quality, and the amount of data to be processed is reduced by compressing the data, and a high speed is provided by providing a buffer. It enables batch writing.

[0008]

When the spatial redundancy of the image is high, the variable length compression improves the compression efficiency and makes it possible to reduce the amount of data to be handled. However, when the variable length compression is used as the compression method, the compression rate differs depending on the complexity and redundancy of the image data. Therefore, the amount of data handled when writing to a storage medium such as a hard disk varies. If the image is complicated and contains a large amount of information, variable-length compression does not improve the compression efficiency. In the worst case,
The amount of data after compression may be equal to or greater than that before compression. Therefore, the size of the buffer memory required to write the compressed data in the storage medium requires a large-capacity memory that is equal to or larger than the amount of data before compression.
Furthermore, by handling data of different sizes depending on the input image data, memory management becomes complicated and it becomes an obstacle when writing to a storage medium.

In the case of this configuration, since there is no memory for storing the input image data as it is, when trying to edit the input data such as rotation and cutout,
You are forced to make edits on the buffer memory that holds the compressed data. However, in the variable-length compressed data, the positional relationship of the original input image pixels has changed in a complicated manner. Therefore, it is possible to directly edit the input image data such as rotation and cutout. It is impossible.

Therefore, the present invention provides an image signal coding apparatus capable of editing image data using a buffer memory having a small capacity and having high image data compression efficiency. With the goal.

[0011]

SUMMARY OF THE INVENTION According to the present invention, image input means for inputting an image to obtain image data and image data obtained from the image input means are kept constant while maintaining a two-dimensional positional relationship. First encoding means for performing fixed-length compression at a compression rate, first storage means for holding a result of compression by the first encoding means, and contents of the first storage means are sequentially read and changed. Second encoding means for performing long compression, second storage means for holding the result of compression by the second encoding means, fixed length compression from the second storage means, and further variable length compression And a storage medium for storing and holding image data.

[0012]

The image data from the image input device is first compressed in fixed length and written in the first storage means. At this point in time, the two-dimensional positional relationship of the image data is retained, so that the image data in the first storage means can be directly manipulated to perform position editing. Next, the fixed-length compressed image data is variable-length compressed and stored in the storage medium via the second storage means. At this point, the image data has been compressed at a high compression rate, so the storage efficiency of the storage medium is high.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic block diagram showing the structure of an image signal coding apparatus according to this embodiment. The image data input from the image input device 201 is input to the fixed length compression circuit 204 via the image quality correction device 202 that corrects the characteristics of the input device by a filter or the like to improve the image quality.

FIG. 2 is a schematic block diagram of the fixed length compression / expansion circuit 204. Here, for the fixed length compression / expansion circuit 204, for example, a combination of discrete cosine transform (DCT) and quantization processing is used. The input image data is divided into blocks each having 8 × 8 pixels, and the DCT calculation circuit 302 performs a two-dimensional DCT calculation for each block to obtain 64 DCT coefficients. The quantization circuit 303 performs coding quantization processing on this DCT coefficient. The DCT coefficient is linearly quantized using the coding quantization table 304 with a different step size for each coefficient position. By appropriately selecting the quantization table 304, it is possible to control the image quality and the amount of coded information of the image to be stored. Therefore, the optimum coded quantization table is selected for each input image characteristic. It is possible.

The quantized data is output to the first buffer memory 205. An image editing device 209 capable of editing in block units is connected to the buffer memory 205. Since the quantization is performed for each 8 × 8 block, the array of the quantized image data is for each block, and the positional relationship of the input image pixels is retained. for that reason,
With the image editing device 209, rotation processing for switching the vertical and horizontal directions of the image data, processing for cutting out a part of the image, or processing for deleting a part of the image,
When editing such as enlarging / reducing processing, it is possible to edit in block units. In this case, it is possible to edit with a smaller data amount than the input data amount. Therefore, it is possible to reduce the memory capacity for one screen required for image editing. The size (storage capacity) of the first buffer memory 205 is a fraction of the maximum capacity of image data that can be input in the image input device 201. If the compression ratio of the fixed length compression / expansion circuit 204 is ⅕, the size of the first buffer memory 205 is ⅕ of the inputtable data size.

Further, the contents of the first buffer memory 205 are input to the variable length compression circuit 206. Here, the variable length compression circuit 206 uses, for example, Huffman coding. Since this is reversible entropy coding, the decoded data maintains the same identity as the data before coding. Therefore, the image stored in the image output device 2
The deterioration of the image quality when output from 03 is only that which occurs during fixed length coding. That is, when considering the entire system of the present invention, the image quality deterioration can be suppressed to the same level as the fixed length coding only. Further, it is possible to further improve the compression efficiency by using the lossy variable length coding.

The compressed data is output to the second buffer memory 207. The data output from the variable length compression circuit 206 is not output all at once, but the processed portions are sequentially output. Second buffer memory 2
The purpose of 07 is to store the entire data after the variable length compression processing. The compression rate of the variable length compression circuit 206 varies depending on the input data, and the compression rate may be 1/1 for complicated input data. Therefore, the size of the second buffer memory 207 is the variable length compression circuit 2
The maximum amount of data that can be input to 06, that is, the size of the first buffer memory 205 must be the same.

Here, when the compression ratio of the fixed length compression is 1/5, the capacity of the first buffer memory 205 is 1/5 of the inputtable data size, and the capacity of the second buffer memory is the first. Since the same amount of buffer memory is used, the required memory capacity is 2/5 of the inputtable data size in the entire system of the present invention.

The contents of the second buffer memory 207 are written and stored in a storage medium 208 such as a hard disk. Here, without providing the second buffer memory 207,
When the results of variable-length compression are sequentially written to the storage medium 208, the number of accesses to the storage medium 208 increases in proportion to the input data size, which significantly increases the processing time. In addition, since the number of access operations increases, it is feared that mechanical fatigue may be caused and durability may be significantly reduced.
Therefore, in the present embodiment, the processing time is shortened by accumulating the variable length compression result in the second buffer memory 207 and writing it to the hard disk at a high speed at once. At this time, the data name is written at the beginning of the data block to improve the search efficiency during image output.

In order to output the data stored in the storage medium 208 from the image output device 203, the above procedure is followed in reverse. A data block corresponding to the image data designated for output is searched on the storage medium 208, the corresponding one is read, and output to the second buffer memory 207. This data is subjected to variable length expansion processing by the variable length compression circuit 206 and output to the first buffer memory 205,
Further, the fixed-length compression / expansion circuit 204 performs fixed-length expansion processing and outputs it to the image quality correction device 202. Image quality correction device 2
In 02, the characteristics of the image output device 203 are corrected, the image quality is improved, and the image is output to the image output device 203.

In order to increase the speed, it is possible to parallelize the same structure as described above.

The input image data is stored in the storage medium 2.
If not stored in 08, the data input from the image input device 201 is output to the image output device 203 as it is via the image quality correction device 202.

[0024]

According to the present invention, editability for an input image can be ensured for fixed-length compressed data, and at the same time, improvement in compression efficiency can be ensured by performing variable-length compression thereafter. Moreover, since the required memory size is also reduced, it is possible to reduce the total cost.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an image signal encoding device in this embodiment.

FIG. 2 is a schematic block diagram showing a configuration of a fixed length compression circuit.

FIG. 3 is a schematic block diagram showing a configuration of an image signal encoding device in a conventional example.

[Explanation of symbols]

101, 201 ... Image input device, 102, 202 ... Image quality correction device, 103, 206 ... Variable length compression device, 105,
205, 207 ... Buffer memory, 106, 208 ... Storage medium, 204 ... Fixed-length compression / expansion device, 209 ... Image editing device, 302 ... DCT arithmetic circuit, 303 ... Quantization circuit, 304 ... Encoding quantization table

Claims (1)

[Claims] 1. An image input unit for inputting an image to obtain image data, and image data obtained from the image input unit is subjected to fixed length compression at a constant compression rate while maintaining a two-dimensional positional relationship. First encoding means, first storage means for holding the result of compression by the first encoding means, second code for sequentially reading the contents of the first storage means and performing variable length compression Encoding means, second storage means for holding the result of compression by the second encoding means, and storage medium for storing and holding fixed-length-compressed and variable-length-compressed image data from the second storage means. An image signal encoding device comprising: