JP2001045488A - Method and device for decoding image and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decode image data encoded by a multi-structure bit stream format in accordance with a request made at the time of decoding. SOLUTION: This image decoding method reads encoded image data S0 encoded by an encoding system using wavelet transformation and inputs the data S0 to a decoding means 2. An inputting means 3 inputs a decoding mode selected from a standard mode, a semi-high speed mode and a high speed mode, and the means 2 decodes the data S0 in accordance with the inputted decoding mode. In the standard mode, for instance, decoded image data S1 are obtained by performing inverse wavelet transformation after performing decoding up to the highest resolution. The obtained decoded image data S1 are inputted to a reproducing means 4 so that the data are reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image decoding method and apparatus for decoding image data encoded in a multi-structure bit stream format using a technique such as a wavelet transform or a DCT transform in a JPEG file format. The present invention also relates to a computer-readable recording medium on which a program for causing a computer to execute an image decoding method is recorded.

[0002]

2. Description of the Related Art Various compression algorithms have been proposed in the field of image data compression in image servers of medical networks and general data compression such as communication and filing. For example, the WTCQ method (P. Sriram and MWMar
cellin, "Image coding using wavelet transforms and
entropy-constrained trellis-coded quantization ", I
EEE Transactions on Image Processing, vol.4, pp.72
5-733, June 1995) or SPIHT method (A. Said
and WAPearlman, "A New Fast and Efficient Image
Codec Based on Set Partitioning in Hierarchical T
rees ", IEEE Transactions on Circuitsand Systems fo
r Video Tech., vol.6, pp.243-250, June 1996) has been proposed. In these methods, first, original image data representing an original image is subjected to wavelet transform to obtain multi-resolution converted image data, the converted image data is classified, and bit allocation is determined. Quantization is performed using the TCQ method to obtain quantized data. Then, encoded image data is obtained by entropy coding the quantized data.

As described above, in the encoding method using the wavelet transform, original image data is converted into image data in a multi-resolution space representing a structure in a plurality of frequency bands, and the encoded image data is It has the bit stream format of the structure.

[0004] DCT transform performed in the general field of JPEG compression is performed by dividing original image data into blocks and then performing discrete cosine transform (DCT).
Then, bit allocation is determined and quantization is performed to obtain quantized data, and the quantized data is encoded to obtain encoded data. In such an encoding method using the DCT transform, data in each block is decomposed into a DC component and an AC component, and the AC component represents a structure from a low frequency to a high frequency in the block. The encoded image data has a multi-structure bit stream format.

[0005]

SUMMARY OF THE INVENTION The present invention relates to an image decoding system capable of decoding encoded data in a desired manner when decoding encoded data in a multi-structure bit stream format as described above. It is an object of the present invention to provide a computer-readable recording medium on which a program for causing a computer to execute the decoding method and apparatus and the image decoding method is recorded.

[0006]

An image decoding method according to the present invention decodes encoded image data obtained by encoding image data in a multi-structure bit stream format to obtain decoded image data. In the decoding method, the degree of the decoding is changed, and the encoded image data is decoded.

Here, "encoding in a multi-structure bit stream format" refers to encoding after converting image data into a multi-resolution space by wavelet transform or DCT transform as described above.

[0008] Further, "changing the degree of decoding" means
In a multi-structure bit stream format, decoding is performed so that it can be reproduced up to the highest resolution that can obtain a high-quality image, or an arbitrary resolution is used so that the calculation time for decoding can be reduced even if image quality is somewhat sacrificed This means that decoding is performed only up to that point. In the case where decoding is performed only up to an arbitrary resolution, enlargement by interpolation to have the same size as the original image data is also included in the “decoding” of the present invention.

In the image decoding method according to the present invention, a plurality of predetermined decoding modes can be selected according to the degree of decoding, and the coded image is selected according to the selected decoding mode. Preferably, the data is decrypted.

[0010] In one of the decoding modes, it is preferable that the degree of the decoding is determined based on a calculation time for the decoding. It is preferable that the degree of decoding is determined based on the image quality of the image obtained by the decoding.

Further, in one of the decoding modes, it is preferable that the degree of the decoding is determined based on the type of output means for outputting the decoded image data. Preferably, the degree of the decoding is determined based on the use of the data.

An image decoding apparatus according to the present invention is an image decoding apparatus for decoding encoded image data obtained by encoding image data in a multi-structure bit stream format to obtain decoded image data. Decoding means for changing the degree of decoding and decoding the encoded image data is provided.

In the image decoding apparatus according to the present invention, the image decoding apparatus further comprises a selecting means for selecting a plurality of predetermined decoding modes according to the degree of the decoding, and the decoding means comprises: It is preferable that the decoding means is means for decoding the encoded image data in accordance with the selected decoding mode.

In the image decoding apparatus according to the present invention, it is preferable that one of the decoding modes determines the degree of the decoding based on an operation time for the decoding. Preferably, the degree of decoding is determined based on the image quality of an image obtained by reproducing the decoded image data.

Further, in one of the decoding modes, it is preferable that the degree of the decoding is determined based on the type of output means for outputting the decoded image data. Preferably, the degree of the decoding is determined based on the use of the data.

The image decoding method according to the present invention may be provided by being recorded on a computer-readable recording medium as a program for causing a computer to execute the method.

[0017]

According to the present invention, the degree of decoding is changed when decoding coded image data coded in the multi-structure bit stream format. Accordingly, the encoded image data can be decoded according to a desired degree of decoding. For example, if you want to reduce the computation time, change the degree of decoding so that decoding is not performed up to the highest resolution, and if you want to obtain a high-quality image, perform decoding up to the highest resolution. The degree of decryption can be changed.

Further, by making the degree of decoding selectable from a plurality of predetermined decoding modes, it is possible to easily change the degree of decoding, thereby facilitating the user's convenience. it can.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic block diagram showing a configuration of an image decoding apparatus according to an embodiment of the present invention. In the present embodiment, description will be made assuming that the coded image data S0 obtained by coding the original image data by the coding method using the wavelet transform is decoded. As shown in FIG. 1, an image decoding apparatus according to the present embodiment includes a storage unit 1 that stores encoded image data S0, and a decoding unit that decodes the encoded image data S0 read from the storage unit 1. An input unit 3 such as a keyboard and a mouse for setting a decoding mode in the decoding unit 2, and a reproducing unit 4 such as a monitor and a printer for reproducing the decoded image data S2 obtained by the decoding. It becomes.

More specifically, the original image data is decomposed into hierarchical data for each hierarchy, encoded and stored in the storage means 1 as follows. First, as shown in FIG. 2A, image data is subjected to wavelet transform and decomposed into four data LL1, HL0, LH0, and HH0 for each of a plurality of resolutions. Here, the data LL1 represents an image obtained by reducing the height and width of the image to half, and the data HL0,
LH0 and HH0 represent images of vertical edge, horizontal edge and oblique edge components, respectively. Then, as shown in FIG. 2B, the data LL1 is further subjected to wavelet transform to obtain four data LL2, HL1, LH1 and HH1. Here, the data LL2 is the data LL1
Of the data HL1, LH1, and HH1 represent images of the vertical, horizontal, and oblique edge components of the data LL1, respectively. Then, the data LL obtained each time the wavelet transform is performed is repeated as many times as desired by the wavelet transform to obtain data for a plurality of resolutions. Thereafter, as shown in FIG. 2C, the data for each resolution is encoded, and the encoded data of each layer is stored in the storage unit 1 as encoded image data S0 composed of one file. .

From the input means 3, three decoding modes of "standard mode", "quasi-high-speed mode" and "high-speed mode" are selectively input. As this input, "standard mode", "quasi-high-speed mode", and "high-speed mode" may be input by number. These modes are displayed on a monitor (not shown), and The mode may be input by clicking the screen of the monitor.

In the "standard mode", the encoded image data S0
Is a mode in which after decoding to the highest resolution, inverse wavelet transform is performed on each of the decoded hierarchical data to obtain decoded image data S1. "Quasi-fast mode"
Is obtained by decoding the coded image data S0 to a half resolution of the highest resolution, inserting 0 as the value of the highest resolution hierarchical data, and performing inverse wavelet transform together with the hierarchical data decoded to 1/2 resolution. Is performed to obtain the decoded image data S1. In the “high-speed mode”, after decoding the encoded image data S0 to a resolution of １ ／ of the highest resolution, the hierarchical data decoded to １ ／ resolution is subjected to inverse wavelet transform to obtain decoded image data. This is a mode in which this is enlarged twice by linear interpolation to obtain decoded image data S1 having the same size as the original image data.

Here, in the standard mode, the quasi-high-speed mode and the high-speed mode, the decoding processing time is as follows: standard mode> quasi-high-speed mode> high-speed mode. The image quality of the image obtained by decoding is as follows: standard mode> quasi-high speed mode> high speed mode, and the standard mode has the highest image quality. In the quasi-high-speed mode and the high-speed mode, decoding is performed only up to 1/2 resolution. However, in the quasi-high-speed mode, the subsequent processing is performed by linear interpolation, and the processing speed is high. The mode is faster, and the image quality is higher in the semi-high-speed mode. Here, a simulation result of a radiation image of the chest by the present applicant is shown below. In Table 1, PS
NR is a value serving as an index of image quality.

[0025]

[Table 1] Next, the operation of the present embodiment will be described. FIG. 3 is a flowchart showing the operation of the present embodiment. First, the encoded image data S0 is read from the storage unit 1 (step S1), and the decoding mode input from the input unit 3 is determined (step S2, step S3). If the input decoding mode is the standard mode, step S
2 is affirmed, and the encoded image data S0 is decoded in the standard mode to obtain the decoded image data S1 (step S4).

On the other hand, if the input decoding mode is the quasi-high speed mode, step S2 is denied and step S3 is affirmed, and the coded image data S0 is decoded in the quasi-high speed mode and decoded. Image data S1 is obtained (step S5). Further, when the input encoding mode is the high-speed mode, steps S2 and S3 are denied, and the encoded image data is decoded in the high-speed mode to obtain the decoded image data S1 (step S2). S6). The obtained decoded image data S1 is provided for playback by the playback means 4 (step S7), and the process is terminated.

As described above, in the present embodiment, the degree of decoding of the coded image data S0 is changed according to the decoding mode input from the input means 3, so that the request at the time of decoding can be satisfied. Accordingly, decoded image data S1 appropriately decoded can be obtained.

The performance differs depending on the apparatus for reproducing the decoded image data S1, and a high-performance apparatus can reproduce a high-quality image, but a low-performance apparatus requires a long time for decoding. Since it takes time, high-quality images cannot be reproduced. For this reason, conventionally, the encoding method of the image data was changed according to the device to be reproduced to obtain encoded image data according to the device, but in this case, it is attempted to reproduce the image on another device. Then, it was necessary to change (transcode) the encoding method to one suitable for another device, which was not efficient. In such a case, by using the image processing apparatus according to the present embodiment, if there is a single piece of encoded image data S0, it is possible to perform decoding by changing the degree of decoding according to the performance of the playback apparatus. This eliminates the need for transcoding.

In the above-described embodiment, the coded image data S0 is obtained by coding the original image data by the layering method by the wavelet transform. However, the coded image data S0 is coded by the DCT method. The structured image data S0 may be used. In this case, in the DCT transform method, original image data is divided into a plurality of blocks, and a DC component and an AC component are created in each block, and these are encoded to obtain encoded image data S0. It is. At this time, since the AC component represents a structure from the low frequency to the high frequency in the block, by changing the degree of decoding the AC component at the time of decoding,
The decoding operation time and the image quality of an image obtained by reproducing the decoded image data S1 can be changed. That is, as shown in FIG. 4, the coded image data S0 in each block is composed of a DC component and an AC component. The image data S1 has high image quality. On the other hand, if the AC component is decoded to an intermediate frequency, the image processing time can be reduced although the image quality is slightly degraded. Therefore, by changing the degree of decoding of the AC component, the degree of decoding can be changed in the same manner as in the above-described embodiment. Decoded image data S
1 can be obtained.

In the above embodiment, three modes of the standard mode, the quasi-high-speed mode and the high-speed mode are selected from the input means 3, but the decoding mode is not limited to this. And only the standard mode and the high-speed mode may be used.
Various modes may be selectable, such as a mode in which decoding is performed at a higher speed such that decoding is performed only up to a resolution of up to 4. Alternatively, the desired degree of decoding may be input from the input means 3 using characters.

Further, in the above embodiment, three modes of the standard mode, the quasi-high speed mode and the high speed mode are selected from the input means 3 to change the degree of decoding. Alternatively, the degree of decoding may be changed according to the output destination of the decoded image data S1. More specifically, “laser printer”
And "CRT monitor", and when "laser printer" is selected, the encoded image data S
0 is decoded to obtain decoded image data S1. On the other hand, a CRT monitor cannot reproduce a high quality image even if the reproduced image data can reproduce a high quality image. Therefore, when the "CRT monitor" is selected as the output destination, the encoded image data S0 may be decoded in the "high-speed mode" capable of decoding at high speed to obtain the decoded image data S1.

When the coded image data S0 is obtained by coding image data representing a radiographic image, it is reproduced because the radiology department needs to observe the radiographic image to make a detailed diagnosis. The image is preferably of high quality. On the other hand, in a clinical department, a radiographic image is used only for reference, so that it is not necessary to have a very high image quality. Accordingly, two decoding modes of “radiology terminal” and “clinical terminal” can be selected as an output destination from the input means 3, and when “radiology terminal” is selected, image quality is emphasized. The encoded image data S0 is decoded by the "standard mode"
1 is obtained, and when "clinical department terminal" is selected, the encoded image data S0 is decoded by the "high-speed mode" capable of high-speed decoding to obtain the decoded image data S1. Is also good.

Further, the degree of decoding may be changed according to the purpose of use of the decoded image data S1. For example, when the coded image data S0 is obtained by coding image data representing a radiation image, when performing a primary diagnosis, it is necessary to observe the radiation image to create a detailed finding. It is preferable that the image to be obtained has high image quality. On the other hand, when performing a diagnosis using a past image such as follow-up observation, a certain image quality is required, but it is not necessary to be as high as the primary diagnosis. In addition, when a radiation image is used for reference, it is not necessary to have a very high image quality. Therefore, the use purpose from the input means 3 is “primary diagnostic use”, “past image diagnostic use”, and “reference use”.
When the "primary diagnostic use" is selected, the coded image data S0 is decoded by the "standard mode" which emphasizes image quality to obtain the decoded image data S1. As described above, when the "past image diagnosis use" is selected, the coded image data S0 is decoded by the "quasi-high speed mode" in which an image of a certain image quality is obtained to obtain the decoded image data S1, When the "reference application" is selected, the encoded image data S0 may be decoded to obtain the decoded image data S1 in a "high-speed mode" in which decoding can be performed at a high speed.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram illustrating a configuration of an image decoding device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a state in which image data is wavelet transformed and encoded for each layer.

FIG. 3 is a flowchart showing the operation of the embodiment.

FIG. 4 is a diagram showing encoded image data obtained by DCT transform;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Storage means 2 Decoding means 3 Input means 4 Reproduction means

Claims (18)

[Claims] 1. An image decoding method for decoding encoded image data obtained by encoding image data in a multi-structure bit stream format to obtain decoded image data, wherein the degree of decoding is changed. And decoding the encoded image data. 2. A method according to claim 1, wherein a plurality of predetermined decoding modes are selectable according to the degree of decoding, and the encoded image data is decoded according to the selected decoding mode. The image decoding method according to claim 1. 3. The image decoding method according to claim 2, wherein one of the decoding modes determines the degree of the decoding based on an operation time for the decoding. 4. The decoding mode according to claim 1, wherein the degree of the decoding is determined based on the image quality of an image obtained by reproducing the decoded image data. Item 3. The image decoding method according to Item 2 or 3. 5. The decoding mode according to claim 2, wherein one of the decoding modes determines the degree of the decoding based on a type of an output unit that outputs the decoded image data. 5. The image decoding method according to claim 4. 6. The method according to claim 2, wherein one of the decoding modes determines the degree of the decoding based on a use of the decoded image data. Item. 7. An image decoding apparatus which obtains decoded image data by decoding encoded image data obtained by encoding image data in a multi-structure bit stream format, wherein the degree of decoding is changed. A decoding means for decoding the coded image data. 8. The image processing apparatus according to claim 1, further comprising a selection unit that selects a plurality of predetermined decoding modes according to a degree of the decoding, wherein the decoding unit selects a plurality of decoding modes according to the decoding mode selected by the selection unit. 8. The image decoding device according to claim 7, wherein the image decoding device is means for decoding the encoded image data. 9. The image decoding apparatus according to claim 8, wherein one of the decoding modes determines the degree of the decoding based on an operation time for the decoding. 10. The decoding mode according to claim 1, wherein the degree of the decoding is determined based on the image quality of an image obtained by reproducing the decoded image data. Item 10. The image decoding device according to Item 8 or 9. 11. The decoding mode according to claim 8, wherein one of the decoding modes determines the degree of the decoding based on a type of an output unit that outputs the decoded image data. 11. The image decoding device according to claim 10. 12. The method according to claim 8, wherein one of the decoding modes determines the degree of the decoding based on a use of the decoded image data. An image decoding apparatus according to any one of the preceding claims. 13. A program for causing a computer to execute an image decoding method for decoding encoded image data obtained by encoding image data in a multi-structure bit stream format to obtain decoded image data. A non-transitory computer-readable recording medium, characterized in that the program has a procedure of changing the degree of decoding and decoding the encoded image data. 14. A method according to claim 1, further comprising a step of selecting a plurality of predetermined decoding modes according to the degree of decoding, wherein the step of decoding includes the step of selecting the coded image in accordance with the selected decoding mode. 14. The computer-readable recording medium according to claim 13, which is a procedure for decoding data. 15. The computer readable recording according to claim 14, wherein one of the decoding modes determines the degree of the decoding based on an operation time for the decoding. Medium. 16. The decoding mode according to claim 1, wherein the degree of the decoding is determined based on the image quality of an image obtained by reproducing the decoded image data. Item 16. A computer-readable recording medium according to item 14 or 15. 17. The method according to claim 14, wherein one of the decoding modes determines the degree of the decoding based on a type of an output unit that outputs the decoded image data. A computer-readable recording medium according to any one of Claims 16 to 16. 18. The method according to claim 14, wherein one of the decoding modes determines a degree of the decoding based on a use of the decoded image data.
A computer-readable recording medium according to any one of the preceding claims.