JP2962722B2 - Decryption device - Google Patents

Description

The present invention divides image information into a plurality of blocks each including a plurality of pixels, and decodes coded data obtained by coding an image of each block for each frequency component. And a decoding device for outputting to a display device.

[Conventional technology]

Conventionally, since image data has an enormous data amount compared to other encoded symbol data, various data compression / encoding methods and transmission methods suitable for storage / storage and data transmission have been proposed. ing.

As an encoding method, it has been proposed to divide image information into a plurality of blocks consisting of a plurality of pixels and encode them in units of blocks in order to enable high-rate compression of a halftone image or a multi-valued image.

In particular, from the viewpoint of data storage / storage, an image coding method that vector-quantizes an image into blocks of a plurality of pixels can achieve performance close to the rate / distortion limit in principle. Therefore, attention has been paid to its high compression ratio.

[Problems to be solved by the invention]

However, in the conventional data compression encoding method, it is not possible to grasp what the image of one screen is unless the encoded data of all of a plurality of blocks constituting one screen is decoded.

Therefore, when searching for a required image from the stored encoded data for a plurality of images, it is necessary to wait for all decodings to determine whether the image represented by the encoded data currently being decoded is the desired image. I could not recognize it.

[Means for Solving the Invention]

The present invention has been made in view of the above points, and has been obtained by converting image data of a block composed of a plurality of pixels into a plurality of frequency components and encoding the image data according to the characteristics of the image of each block. A decoding device for receiving data and displaying the data on a predetermined display device, receiving encoded data of a first frequency component, decoding the first frequency component using inverse orthogonal transform, (1) decoding means for outputting decoded data, storage means for storing the first decoded data output by the decoding means, and reception of a second frequency component having a higher frequency than the first frequency component Then, the second decoding data obtained by decoding the second frequency component by using the inverse orthogonal transform by the decoding means and the first decoded data obtained by reading from the storage means are actually executed. Combining means for combining in image space; A first display to be displayed based on the first decoded data obtained by reading from the storage means is performed by the predetermined display device, and when the second frequency component is received, an actual image of the synthesis means is displayed. Display control means for causing the predetermined display device to perform a second display for displaying a synthesized image obtained by synthesis in a space.

FIG. 1 shows a schematic configuration of an image encoding apparatus to which the present invention is applied.

Reference numeral 1 denotes an orthogonal exchange unit that performs orthogonal transformation on an image input from the signal line 10 for each block (in this embodiment, a unit block is 4 × 4 pixels). In this embodiment, the orthogonal transform is 4
A Hadamard transform of × 4 pixels is used. By this Hadamard transform, each block image having 4 × 4 pixels as a unit block is converted into 16 conversion coefficients (Y ₁₁ , Y ₁₂ ,..., Y ₄₄ ). Reference numeral 11 denotes a signal line for these conversion coefficients. FIG. 2 is a conceptual diagram of the Hadamard transform. 4 × 4 in FIG. 2 (a)
The pixel data X ₁₁ , X ₁₂ ,..., X ₄₄ are subjected to Hadamard transform, and the second
Conversion to the sequence components of Y ₁₁ , Y ₁₂ ,..., Y ₄₄ in FIG. Y _{11 to} Y ₄₄ are components corresponding to the sequence at the same position in FIG. As can be seen from the figure, a higher i, j value of Y _ij indicates a higher frequency component.

Each component Y ₁₁ after orthogonal transformation output from the orthogonal transformation unit 1
The to Y _44, bands divided as in Figure 4. FIG. 4 (a)
4 shows an example of 4-band division, and FIG. 4B shows an example of 3-band division. Taking the three-band division of FIG. 4 (b) as an example, Y ₁₁ , Y
The three components of ₁₂ and Y ₂₁ are the first as band 1 (low frequency band).
Of the sub-block. Y ₁₃ , Y ₁₄ , Y ₂₂ , Y ₂₃ , Y ₃₁ , Y
_32, 7 components of Y ₄₁ constitute a second, third sub-block as well as a band 2 (intermediate frequency band), the other component band 3 (high frequency band).

Reference numeral 4 in FIG. 1 denotes a vector quantizer, which performs vector quantization on the output from the orthogonal transform unit 1 for each of the three sub-blocks described above. The vector quantizers 4a to 4c for the three bands are configured completely independently. By dividing the vector quantizer into these three bands,
The number of dimensions is reduced, and the scale of the quantizer can be reduced.

The vector quantizers 4a to 4c are constituted by a look-up table constituted by a ROM or the like so as to select an optimum reproduction vector when an input vector is input. Here, it is assumed that the optimum reproduction vector has been obtained from the training data divided into each band in advance.

Reference numeral 2 in FIG. 1 denotes a class classification unit for analyzing Y ₁₁ to Y ₄₄ from the orthogonal transformation unit 1 and classifying each block according to frequency.
The class classification unit 2 classifies the blocks into four classes for each frequency and outputs the result to the signal line 12 as classification information composed of two bits of data.

FIG. 5 shows a classification method in the classification unit 2.

 Here, it is defined as follows.

These E1, E2 and E3 are average values for each band shown in FIG. 4 (b).

As shown in FIG. 5, if E1.gtoreq.T1 (T1 is a threshold), the signal is classified into class 1 (flat portion) as a low-frequency class. Furthermore, if E2≥T2, it is class2 (medium edge) as a medium frequency class, and if E3≥T3, it is class3 as a high frequency class
(Large edge) E1 ≧ T1, E2 ≧ T2 and E3
Those that do not satisfy ≧ T3 have lower power of all bands
Classify as a flat part of class1.

When such a classification is made, the class in which the power of the high frequency component is large, that is, the high frequency class is set so that the number of data bands to be transmitted is increased.

That is, as shown in FIG. 6, only the information of band 1 (low-frequency component vector quantized data) having a data length of 1 bit for class 1 (flat portion), and the data length for class 2 (middle edge). 1-bit band 1 information and data length m-bit band 2 information (middle frequency component), and class 3 information with l, m, n-bit band 1, band 2 and band 3 information (high ).

In this way, a high compression rate can be expected by classifying and band-dividing each block after the orthogonal transformation and adaptively encoding according to the image quality. This is because normal image information has many flat portions of class 1 represented by a short data length. As shown in FIG. 6, a class code is added to the head of each class of data as an index. When classifying into three classes, a 2-bit class code is required. Class1: Class code = 00 (binary display) class2: 〃 = 01 (〃) class3: 〃 = 10 (〃) You.

In some of the embodiments described later in this specification, the class code of class3 may be represented as “11” for convenience.
The length of the class code changes correspondingly according to the number of classifications.

Reference numeral 6 in FIG. 1 denotes a sequencer. Next, the function of the sequencer 6 will be described.

The reproduction vectors 5a to 5c of each band obtained by the vector quantizers 4a to 4c are transmitted for each band by the sequencer 6 based on the classification information 12 compiled for each band.

Figure 7, for each block of the two-dimensional image data and block divided into B ₀₀ .about.B _mn shows the results of the classification of the above. (A) shows the number of each block, and (b) shows the result of classifying the block.

FIG. 8 shows a procedure for transmitting data obtained by encoding the image shown in FIG. 7 (a). In STEP1 constituting the one screen to transmit information of the band 1 of the total block B ₀₀ .about.B _mn. Then, information of band 2 is transmitted in STEP2, and information of band 3 is transmitted in STEP3.

In STEPs 2 and 3, it is not necessary to send the band information of all of the blocks constituting one screen. For this reason, information of band 2 for blocks of class 2 and class 3 and information of band 3 for blocks of class 3 are transmitted only to blocks at necessary places.

For each such block, a band from steps 2 and 3
Information on whether or not transmission of band 2 information is necessary
At the time of transmitting the information of band 1 in the above, the class code is added to the information of band 1 of each block and transmitted for the total number of blocks. Then, this class code is stored for each block on the receiving side, and the information of band 2 and the information of band 3 are picked up only at a portion (block) where high band information is required by referring to the class code.

FIG. 9 shows the signal processing method on the receiving side. As the reception signal 20, information for each band of each block is input in the order of STEP shown in FIG.

When the class code is transmitted together with the band 1 information in STEP 1, the class code is stored in the class code memory.
Stored temporarily in 21. The received code 20 is converted to real space data by the inverse Hadamard converter 22 and the real data output
Output as 23. The actual data output 23 is supplied to, for example, an image memory 24 or the like. An image based on the image data stored in the memory 24 is displayed on the display 25.

In STEPs 2 and 3, the processing for the received signal 20 differs according to the contents of the class code memory 21. The contents to be processed according to the contents of the class code are as follows: When the class code = 1 (00 in binary), there is no high band component of the block, and therefore, it is skipped.

When class code = 2 (01 in binary) Only the information of band 2 is subjected to inverse Hadamard transform.

When the class code is 3 (10 in binary), the information of the band 3 and the band 2 is subjected to the inverse Hadamard transformation. Therefore, the sequentially transmitted high band codes (the information of the band 1 and the band 3) are By collating with the contents, it is recognized as the target block information.

As described above, the information transmitted for each band is inversely transformed independently for each band, and is added to the previous inverse transformation value already stored in the memory 24 for each block. As a result, a final decoded image can be obtained.

FIG. 10 shows the configuration of the inverse Hadamard transformer 22 and the memory 24 in FIG.

An expander 31 expands the data input from the signal line 41 into blocks. At this time, the class code is sent from the class code memory 21 to the 42 signal lines, and the 32
The ROM defines the spectral position of the input band. 33
Is an inverse converter, 34 is an adder, 35 is an image storage unit, and 43, 44, and 45 are buses.

In FIG. 10, the class code sent to the signal line 42 enters the ROM 32, and outputs the position information of the code input from the signal line 41 in the 4 × 4 spectral space to the expander 31. According to this information, the expander 31 leaves only the transmitted band information, and generates a 4 × 4 spectrum masked with 0 for the others.

The generated 16 pieces of data enter the inverse transformer 33, become information in the real image space, and are stored in the storage unit 35 via the adder 34. If there is image information of another band reproduced and stored in the storage unit 35 before this information, it is called from the storage unit 35 and added together with the information from the inverse converter 33.
Enter 34. The addition result in the real image space is a bus
The data is stored in the storage unit 35 again via the line 45.

The image data stored in the storage unit 35 is displayed on the display 25 in this manner. Therefore, Display 25 has
First, the image of band 1, that is, the image of the low frequency component is displayed, and the image to be decoded is roughly displayed. Then, the image of the medium frequency component of band 2 and then band 3
Are superimposed and displayed.

Therefore, it is possible to roughly recognize the image content before decoding all the encoded data constituting one screen.

In the above-described embodiment, the Hadamard transform is used as the frequency transform method, but the present invention can be implemented by using other orthogonal transforms such as cosine transform and KL transform. The order of transmitted bands is not limited.

(Effect)

As described above, according to the present invention, it is possible to display a rough image content without receiving all the encoded data.

In particular, since the present invention converts the image data in the real image space of each block into a plurality of frequency components in the frequency space and then decodes the encoded data encoded from the low-frequency components, the multi-valued block image is encoded. In this case, the decoding device can check the approximate density in the block from the beginning, so that it is possible to quickly and easily determine whether the image is a character image such as a document or a natural image such as a photograph.

In addition, since the first and second frequency components that are separated in the frequency space and hierarchically encoded and transmitted are synthesized in the real image space instead of the frequency space, the synthesis in the frequency space, which had to be performed conventionally, is performed. You don't have to. That is, there is no need to once convert decoded data in the real image space corresponding to the first frequency component into frequency components, and then combine the decoded data with the second frequency component in the delayed frequency space. Hierarchical decoding can be performed.

Further, the encoded data to be received is encoded according to the characteristics of the image for each block, so that the characteristics of the image indicated by the decoded data can be confirmed at an early stage.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of the configuration of an encoding apparatus to which the present invention is applied, FIG. 2 is a conceptual diagram of Hadamard transform, FIG. 3 is a diagram showing sequence components, and FIG. 4 is a diagram showing an example of band division. , FIG. 5 shows a classification procedure, FIG. 6 shows coded data, FIG. 7 shows an example of image classification, and FIG. 8 shows a transmission format of the coded data. , Ninth
FIG. 10 is a diagram showing an example of a processing block on the receiving side, FIG. 10 is a diagram showing a partial detail of the block shown in FIG. 9, 1 is an orthogonal transformation unit, 2 is a class classification unit, 4 is a vector quantizer, and 22 is An inverse Hadamard transform unit, 34 is an adder, and 35 is a storage unit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshihiro Ishida 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Mitsuru Maeda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Naoto Kawamura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-55-134576 (JP, A) JP-A-58-17763 (JP) , A) JP-A-1-141481 (JP, A)

Claims (1)

(57) [Claims] An image data of a block composed of a plurality of pixels is converted into a plurality of frequency components, and encoded data obtained by encoding according to the characteristics of an image of each block is received and displayed on a predetermined display device. Decoding means for receiving encoded data of a first frequency component, decoding the first frequency component using inverse orthogonal transform, and outputting first decoded data; and Storing means for storing the first decoded data output by the decoding means; receiving a second frequency component having a higher frequency than the first frequency component; Second decoded data obtained by decoding frequency components using inverse orthogonal transform, and first decoded data obtained by reading from the storage means.
Synthesizing means for synthesizing the decoded data in a real image space; and causing the predetermined display device to perform a first display based on the first decoded data obtained by reading from the storage means, Display control means for causing the predetermined display device to perform a second display for displaying a combined image obtained by combining in the real image space by the combining means when the second frequency component is received. Decoding device.