JPH0818965A - Method and device for decoding image data - Google Patents

Abstract

PURPOSE:To reduce the deterioration in picture quality on a decoding side when image data is transferred by hierarchically encoding. CONSTITUTION:Decoder means 61-65 which decode image encoded data D51-D55 and smoothing means 70-73 which smooth the block boundaries of decoded data D61-65 obtained by the decoder means 61-65 are provided. In this way, it is possible to eliminate a pseudo contour appearing in the block boundary in the decoded data D61-D65 and to avoid the deterioration in the picture quality.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Industrial Application Conventional Technology (FIGS. 11 and 12) Problem to be Solved by the Invention Means for Solving the Problem (FIGS. 8 to 10) Action (FIGS. 8 to 10) Example (1) Hierarchy Encoding Principle (FIGS. 1 to 3) (2) Hierarchical Coding Device (FIGS. 4 to 7) of Embodiment (2-1) Configuration (2-2) Division Processing (3) Image Decoding of Embodiment Apparatus (FIGS. 8 to 10) (3-1) Configuration (3-2) Smoothing processing (4) Operation of the embodiment (FIGS. 8 to 10) (5) Effect of the embodiment (FIGS. 8 and 9) (6) Other Examples Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data decoding method and apparatus, and is particularly suitable for application when decoding hierarchically encoded data.

[0003]

2. Description of the Related Art Conventionally, there is an image coding apparatus which creates image data for a plurality of layers having different resolutions from input image data and codes the image data. This type of image coding apparatus is configured to hierarchically code input image data by using a hierarchical coding method such as pyramid coding. That is, in this image encoding device, high-resolution input image data is used as first layer data, second resolution data having a lower resolution than the first layer data, and second image data.
Third layer data, which has a lower resolution than the resolution data of
... are sequentially and recursively formed, and these plural hierarchical data are combined into 1
Transmission is performed by one communication path or a transmission path that is a recording / reproducing path.

Further, in the image decoding apparatus for decoding the plurality of hierarchical data, in addition to decoding all of the plurality of image data, any one of the hierarchical data can be obtained depending on the resolution of the television monitor corresponding to each of them. One of them may be selected and decoded. Thus, by decoding only the desired hierarchical data from the plurality of hierarchical data, it is possible to obtain the desired image data with the minimum required transmission data amount.

As shown in FIG. 11, in an image coding apparatus 1 which realizes, for example, four-layer coding as this hierarchical coding, thinning filters 2, 3, 4 for three stages and interpolation filters 5, 6, respectively. 7 and the reduced image data D2, D3, D4 having a sequentially lower resolution are formed by the thinning filters 2, 3, 4 of the respective stages for the input image data D1 and the reduced images are generated by the interpolation filters 5, 6, 7. Data D
2. Return D3, D4 to the resolution before reduction.

Outputs D2 to D4 of the thinning filters 2 to 4
And the outputs D5 to D7 of the respective interpolation filters 5 to 7 are input to the difference circuits 8, 9 and 10, respectively, whereby difference data D8, D9 and D10 are generated. As a result, in the image encoding device 1, the amount of hierarchical data is reduced and the signal power is reduced. Here, this difference data D8
The area of each of D10 to D10 and the reduced image data D4 is 1,
The sizes are 1/4, 1/16 and 1/64.

The difference data D8 to D10 obtained from the difference circuits 8 to 10 and the reduced image data D4 obtained from the thinning filter 4 are encoded by the encoders 11, 12, 13, and 14 and compressed. As a result, the first, second, third and fourth hierarchical data D11, D12, D13 having different resolutions from the respective encoders 11, 12, 13, 14 are applied.
And D14 are sent to the transmission line in a predetermined order.

The first to fourth hierarchical data D11 to D14 thus transmitted are decoded by the image decoding device 20 shown in FIG. That is, the first to fourth hierarchical data D11 to D14 are respectively decrypted by the decoders 21, 22, and
As a result, the fourth layer data D24 is output from the decoder 24.

The output of the decoder 23 is the fourth hierarchical data D obtained from the interpolation filter 26 in the adder circuit 29.
It is added with the interpolation data of 24, whereby the third hierarchical data D23 is restored. Similarly, the output of the decoder 22 is added to the interpolation data of the third hierarchical data D23 obtained from the interpolation filter 27 in the adder circuit 30, whereby the second hierarchical data D22 is restored. Further, the output of the decoder 21 is output by the adder circuit 31 to the interpolation filter 2
8 is added to the interpolated data of the second hierarchical data D22 to restore the first hierarchical data D21.

[0010]

However, in the image coding apparatus which realizes such a hierarchical coding method, since the input image data is divided into a plurality of hierarchical data for coding, only the hierarchical component data is inevitably obtained. The amount increases, and the compression efficiency is correspondingly reduced as compared with the high efficiency coding method that does not use the hierarchical coding. Further, when trying to improve the compression efficiency, there is a problem that image quality deterioration occurs on the decoding side.

The present invention has been made in view of the above points, and proposes an image data decoding method and apparatus capable of reducing image quality deterioration when image data is hierarchically encoded and transmitted. .

[0012]

In order to solve such a problem, in the present invention, by reducing the resolution of each predetermined block of a lower layer having a higher resolution, a block in an upper layer having a lower resolution corresponding to the block is reduced. To generate a plurality of layer image data D31 to D35 having different resolutions sequentially from the lower layer, and the layer obtained by the image encoding device 40 that encodes the plurality of layer image data D31 to D35. Encoded data D51 to D5
In the image data decoding device 60 for decoding 5, the decoding means 61 to 6 for decoding the hierarchically encoded data D51 to D55.
5 and hierarchical decoded data D obtained by the decoding means 61 to 65
Smoothing means 7 for smoothing the block boundaries 61 to D64.
0-73.

In the present invention, the smoothing means 70-
Reference numeral 73 includes a first level detecting means 101 for detecting a level fluctuation in the block, and a second level detecting means 102 for detecting a level fluctuation between pixels across the blocks. The smoothing process is selected based on the detection results S2 and S3 by the second level detecting means 101 and 102.

[0014]

The smoothing means 70 smoothes the block boundaries of the hierarchically decoded data D61 to D64 decoded by the decoding means 61 to 65.
To 73, the pseudo contours appearing at the block boundaries of the hierarchically decoded data D61 to D64 can be effectively avoided, and the image quality deterioration can be reduced.

Further, a first level detecting means 101 for detecting a level fluctuation within the block and a second level detecting means 10 for detecting a level fluctuation between pixels across the blocks.
2 and the smoothing process is selected based on the detection results S2 and S3 by the first and second level detecting means 101 and 102, thereby saving important information such as edges and blocking boundaries. The pseudo contour appearing in can be effectively avoided.

[0016]

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

(1) Principle of Hierarchical Coding FIG. 1 shows, as a whole, the principle of hierarchical coding according to the present invention in which a still image such as a high definition television signal is hierarchically coded and compressed. In this hierarchical encoding, the upper layer data is created by a simple arithmetic average of the lower layer data, thereby realizing a hierarchical structure without an increase in the amount of information.
For decoding from the upper layer to the lower layer, the amount of information in the flat portion is reduced by adaptively controlling the division based on the activity of each block. Further, in the encoding of the differential signal performed for the lower layer, the efficiency is improved by switching the quantization characteristic for each block without additional code based on the activity of the upper layer.

That is, in the hierarchical structure of this hierarchical encoding,
First, the high-definition television signal to be input is defined as the lower layer, and the four pixels X1 to X4 in the small block of 2 lines × 2 pixels in this lower layer are expressed by the following equations.

[Equation 1] The arithmetic mean represented by is taken, and its value m is taken as the value of the upper hierarchy. In this lower hierarchy,

[Equation 2] As shown in, the difference value from the upper layer is prepared for three pixels, so that the hierarchical structure is configured with the same information amount as the original four pixel data.

On the other hand, when decoding the lower hierarchy, 3 pixels X1
~ X3 is the following formula

(Equation 3) As shown by, each difference value Δ is added to the average value m of the upper hierarchy.
Xi is added to obtain the decoded value E [Xi], and the remaining one pixel is

[Equation 4] As shown by, the decoded value E [X4] is determined by subtracting the three decoded values of the lower layer from the average value m of the upper layer. Here, E [] means a decoded value.

In this hierarchical coding, one block is divided into four in order from the upper layer to the lower layer, and accordingly, the data amount is quadrupled for each layer, but is flat. The department reduces redundancy by prohibiting this division. A flag for instructing the presence / absence of this division is prepared for each bit and block. The necessity of division in the lower layer is determined as local activity, for example, the maximum value of the difference data.

Here, as an example of hierarchical coding, HD of ITE is used.
FIG. 2 shows the adaptive division result when the standard image (Y signal) is used and five-layer coding is performed. The ratio of the number of pixels in each layer to the original number of pixels when the threshold value for the maximum difference data is changed is shown, and it can be seen that redundancy is reduced based on the spatial correlation. The reduction efficiency changes depending on the image, but if the threshold value for the maximum difference data is changed from 1 to 6, the average reduction rate becomes 28 to 69 [%].

In practice, the resolution of the upper layer is quadrupled to form a lower layer, and at this time, by encoding the difference data from the upper layer data, the signal level width can be effectively reduced. FIG. 3 shows the case of five layers by the layer coding described above with reference to FIG. 2, but here, the layers are named from the lower layers to the first to fifth layers.

Compared to the 8-bit PCM data of the original image,
A reduction in signal level width can be seen. First with a large number of pixels
Since the ~ 4 layers are differential signals, a significant reduction can be achieved and efficiency is improved by subsequent quantization. As can be seen from the table of FIG. 3, the reduction efficiency has little dependence on the pattern, and is effective for all pictures.

By forming the upper layer with the average value of the lower layer, the error propagation is stopped in the block, and the lower layer is converted into the difference from the average value of the upper layer, so that the efficiency is also provided. You can In actual upper layer coding, there is a correlation in the activities between layers at the same spatial position, and by determining the quantization characteristic of the lower layer from the quantization result of the upper layer, adaptive quantization that does not require additional code Can be realized.

Practically, various HD standard images (8) are obtained by hierarchically encoding an image based on the above-described five-stage hierarchical structure and expressing it in multi-resolution, and performing adaptive division and adaptive quantization using the hierarchical structure. Y / PB / PR of bit is about 1 /
It can be compressed to 8. The additional code for each block prepared for adaptive division is run-length coded in each layer to improve compression efficiency. In this way, an image with sufficient image quality can be obtained in each layer, and a good image without visual deterioration can be obtained even in the final lowest layer.

(2) Hierarchical Coding Device of Embodiment (2-1) Configuration In FIG. 4, reference numeral 40 denotes a hierarchical coding device, and a hierarchical coding encoder section 40A for hierarchically coding and outputting input image data D31. It is configured by a generated information amount control unit 40B which controls so that the generated information amount in the hierarchical coding encoder unit 40A becomes a target value. The hierarchical encoding encoder unit 40A is composed of a data delay memory M1 (FIG. 5) and an encoder. Of these, the memory M1 is provided in the input stage so that the data can be delayed so that the encoding process is not executed until the optimum control value is determined by the generated information amount control unit 40B.

On the other hand, the generated information amount control unit 40B inputs the input image data D31 and sets the optimum control value S1 which is suitable for the data to be processed, and this is set to the hierarchical encoding encoder unit 4
By transmitting the data to 0A, the hierarchical coding encoder unit 40A can perform efficient coding. This is a so-called feedforward buffering configuration.

The hierarchical coding encoder section 40A has the configuration shown in FIG. 5, and in this example, it is adapted to generate the compression coded image data D51 to D55 of five layers having different resolutions.

First, the input image data D31 is input to the first difference circuit 41 and the first averaging circuit 42 via the memory M1. The first averaging circuit 42 generates the second layer data D32 by averaging four pixels of the input image data D31 (that is, the first layer data (the lowest layer data)). In the case of this embodiment, the first averaging circuit 42 inputs the input image data D3 as shown in FIGS. 6D and 6E.
The four pixels X1 (1) to X4 (1) of 1 generate the pixel X1 (2) of the second hierarchical data D2.

Similarly, the pixels X2 (2) to X4 (2) adjacent to the pixel X1 (2) of the second layer data D32 are also the first layer data D.
It is generated by calculating the four-pixel average of 31. Second
The hierarchical data D32 is input to the second difference circuit 43 and the second averaging circuit 44, and the second averaging circuit 44 outputs the second averaging circuit 44.
The third layer data D is obtained by averaging four pixels of the layer data D32.
33 is generated. For example, the pixels X1 (2) to X4 (2) of the second layer data D32 shown in FIGS. 6C and 6D are used to generate the pixel X1 (3) of the third layer data D33, and the pixel X1 (3) is generated. The pixels X2 (3) to X4 (3) adjacent to 3) are also generated by the four pixels of the second hierarchical data D32.

The third layer data D33 is the third difference circuit 4
5 and the third averaging circuit 46, and the third averaging circuit 46 calculates the four-pixel average of the third layer data D33 as shown in FIGS. 6B and 6C, as in the case described above. ,
The fourth layer data D34 including the pixels X1 (4) to X4 (4) is generated. The fourth layer data D44 is input to the fourth difference circuit 47 and the fourth averaging circuit 48, and the fourth averaging circuit 4
8 produces | generates the 5th hierarchy data D35 used as the highest hierarchy by 4 pixel average of the 4th hierarchy data D34. That is, as shown in FIGS. 6A and 6B, the fourth layer data D
The four pixels X1 (4) to X4 (4) of 34 are averaged to generate the pixel X1 (5) of the fifth hierarchical data D35.

Here, the first to fifth hierarchical data D31 to D3
As for the block size of 5, when the block size of the first layer data D31 which is the lowest layer is 1 line × 1 pixel, the second layer data D32 is 1/2 line × 1/2 pixel, and the third layer data D33 is 1/4 line × 1/4 pixel, the fourth layer data D34 is 1/8 line × 1/8 pixel, and the fifth layer data D35 which is the highest layer data is 1
/ 16 line × 1/16 pixel.

The hierarchical coding encoder section 40A repeats the recursive processing in order from the highest hierarchical data (that is, the fifth hierarchical data D35) among the first to fifth hierarchical data D31 to D35 and the two adjacent data. The difference between the hierarchical data is obtained by the difference circuits 41, 43, 45 and 47,
Only the difference data is compression-encoded by the encoders 51-55. As a result, the hierarchical encoding encoder unit 40A compresses the amount of information transmitted on the transmission path.
In order to keep such a compression condition optimum, the hierarchical coding encoder unit 40A decodes the compressed coded data D51 to D55 obtained for each hierarchical layer by the decoders 56 to 59.

That is, the decoder 5 corresponding to the highest layer
Reference numeral 9 restores the compression-encoded data D55 compression-encoded by the encoder 55 to obtain decoded data D48 corresponding to the fifth layer data D35, and supplies this to the fourth difference circuit 47.

On the other hand, the decoder 58 decompresses the compression coded data D54 to obtain decompressed data D47 similar to the fourth layer data D44, and supplies this to the third difference circuit 45. Similarly, the decoder 57 restores the compression encoded data D53 and restores the restored data D4 similar to the third layer data D43.
6 is given to the second difference circuit 43. Also, the decoder 56 restores the compression encoded data D52 to obtain the restored data D45 similar to the second layer data D42,
To the difference circuit 41.

The inter-layer difference data D41 to D44 obtained by the difference circuits 41, 43, 45 and 47 are compression-encoded by the encoders 51 to 54, respectively. At this time, the encoders 51 to 54 compare the activity of each block with a predetermined threshold value. Here, the activity is the difference data D41 to D between the layers when the lower layer data area corresponding to the upper layer data is defined as "block".
Maximum error within block, average error within block, sum of absolute values within block, standard deviation within block of 44 predetermined blocks,
It is a correlation value that represents the sum of n powers in a block or the data frequency above a threshold value in a block. That is, when the activity is low, this block can be called a flat block.

At this time, the encoders 51 to 54, when the block activity is higher than a predetermined threshold value, set this block as a divided block, and select a division process in an adjacent lower hierarchical block spatially corresponding to the block. To do.
For example, for a block for which division processing is selected by the encoder 54, the following encoder 53 compression-codes the inter-layer difference data D43 corresponding to this block as it is, and at the same time, a division determination flag indicating that this block is a division block. Attach and transmit.

On the other hand, if the block activity is less than the predetermined value, the encoders 51 to 54 treat this block as a non-divided block and stop the division process in the adjacent lower hierarchical block spatially corresponding to the block. To do. For example, with respect to a block determined to be discontinued by the encoder 54, the subsequent encoder 53 excludes the inter-layer difference data D43 corresponding to this block from the encoding target, and at the same time, this block is a non-divided block. Is transmitted with a non-division determination flag indicating. This non-divided block is replaced with upper layer data on the decoding device side.

(2-2) Division Processing Next, concrete signal processing by the hierarchical encoding encoder section 40A will be described. In the hierarchical encoding encoder unit 40A, as described above, the inter-layer difference data D41 to D44.
The division selection processing is executed based on the block activity for each predetermined block. In the case of the embodiment, each block is composed of 2 lines × 2 pixels.

Here, the data value of each pixel is X, and the hierarchy of the data value X is represented by a suffix. That is, when the upper layer data is Xi + 1 (0), the adjacent lower layer data can be represented as Xi (j) (j = 0 to 3). Therefore, the inter-tier difference data value ΔXi (j) is

(Equation 5) Can be represented by

The encoders 51 to 54 compare the block activity and the threshold value for each block, and select whether to divide this block in the lower hierarchy or not to divide it based on the comparison result. That is, in the encoders 51 to 54, the division in the lower layer is executed when the block activity is equal to or more than the threshold, whereas the division in the lower layer is stopped when the block activity is less than the threshold.

As a result, the hierarchical encoding device 40 does not have to send the data of the adjacent lower layer corresponding to this block for the block having a low block activity, and the transmission information amount can be reduced accordingly. Incidentally, a 1-bit judgment flag is used as the judgment flag indicating the judgment result of division or non-division.

The threshold value used in the block activity determination in each of the encoders 51 to 54 is the generated information amount control unit 4
It is set according to the optimum control value S1 sent from 0B. That is, as the threshold value increases, the number of non-divided blocks (non-transmission block) increases, and the amount of transmission information decreases. In this way, the hierarchical encoding encoder unit 40
In A, compression coding is performed in order from the upper layer data having a lower resolution, and at this time, the activity is determined for each predetermined block of each layer data, and the block having the lower activity corresponds to this block in the adjacent lower layer. It is designed not to send image data to be used.

Further, in the hierarchical coding system in the embodiment,
A method is used in which the judgment flag is not reflected in the judgment in the subsequent lower layers (hereinafter referred to as an independent judgment method). That is, in the independence determination method, division selection processing based on the threshold value determination is performed every time for each layer independently. For example, even for a block for which non-division determination has been performed once, the activity determination is performed again in the subsequent lower layer, and it is selected here whether to divide again or not. As a result, in the hierarchical coding method using the independent judgment method, the hierarchical coding with less image quality deterioration can be realized without being affected by the judgment flag of the lower hierarchy in the upper hierarchy.

Here, FIG. 7 shows a flow chart of the hierarchical coding processing by the hierarchical coding device 40.
"4" in the hierarchy counter I that stores the hierarchy number in 2
Is registered, and the frame of this hierarchical coding is determined.

Further, in step SP3, the generated information amount control section 40B calculates the generated information amount to generate hierarchical data, and in the following step SP4, each block activity is detected. Generated information amount control unit 40
B determines the optimum control value S1 in step SP5 based on this activity.

Further, in step SP6, the hierarchical coding encoder section 40A executes hierarchical coding based on the optimum control value S1. That is, 5 which is the highest layer at the beginning
Encoding and decoding are performed on the hierarchical data. This result becomes the initial value of the processing in the lower layer, and the difference value between layers with the lower layer is generated in step SP7. Further, in step SP8, division selection and encoding in the lower hierarchy are executed based on the optimum control value S1 determined in step SP5.

After each layer processing, the layer counter I is decremented in step SP9. And step S
In P10, the end determination is performed on the contents of the hierarchy counter I. If not completed, the lower layer processing is continued. When the processing of all layers is completed, the loop is exited and the layer encoding processing is completed in step SP11.

(3) Image Decoding Device of the Embodiment (3-1) Configuration The first to fifth signals thus transmitted together with the division determination flag.
The compression-coded data D51 to D55 of the layers are decoded by the image decoding device 60 as shown in FIG. That is, the first to fifth layer compression encoded data D51 to D55
Are decoders 61, 62, 6 having a decoding method reverse to that of the encoders 57, 55, 53, 51 and 49, respectively.
3, 64 and 65 are input. As a result, the decoders 61 to 61
The inter-tier difference data D56 to D59 of the first to fourth hierarchies respectively decoded by 64 are input to the first to fourth adder circuits 66 to 69, respectively.

Further, the fifth layer compression coded data D55 is decoded by the decoder 65, and the resulting fifth layer data D60 is output as it is and the fourth addition circuit 6 is also provided.
9 is sent. The fourth adding circuit 69 adds the fifth layer data D60 and the fourth layer inter-layer difference data D59 to restore the fourth layer data D64, and sends this to the fourth post-processing circuit 73 and at the same time. 3 to the adder circuit 68.

Similarly, the third adder circuit 68 adds the fourth layer data D64 and the inter-layer difference data D58 of the third layer to restore the third layer data D63, and this is added to the third post-processing circuit. It is sent to the second addition circuit 67 as well as to the second addition circuit 67. Similarly, the second and first adding circuits 67
And 66, the second layer data D62 and the first layer data D61 are restored, and these are sent to the second and first post-processing circuits 71 and 70, respectively.

The first to fourth post-processing circuits 70 to 73 examine the contents of the hierarchical data D61 to D64, respectively, and then adaptively perform smoothing processing to form pseudo contours at block boundaries. It is designed to be removed. That is, in the above-described hierarchical encoding device 40, since inter-layer block division processing is introduced, a pseudo contour may occur along the block boundary depending on the threshold value used in block division. Therefore, the first to fourth post-processing circuits 70-
73 effectively removes the pseudo contour generated on the decoding side by the smoothing process to smooth the smoothed data D71 to D71.
Generate D74.

(3-2) Smoothing processing Here, the post-processing circuits 70 to 73 are configured as shown in FIG. Since the post-processing circuits 70 to 73 have the same configuration, the post-processing circuit 70 will be described below. The post-processing circuit 70 inputs the first layer data D61 output from the addition circuit 66 to the smoothing circuit 100 and the threshold value determination circuits 101 and 102.

The threshold value judgment circuit 101 uses the first layer data D
The intra-block data fluctuation of 61 (that is, intra-block activity) is obtained, this is compared with a predetermined threshold value, and the comparison result is sent to the smoothing circuit 100 as a comparison result signal S2. Further, the threshold determination circuit 102 obtains a block-to-block data difference at the block boundary of the first layer data D61, compares this with a predetermined threshold, and sends the comparison result to the smoothing circuit 100 as a comparison result signal S3. The smoothing circuit 100 selects pixels to be smoothed based on the comparison result signals S2 and S3.

Practically, the post-processing circuit 70 inputs the first layer data D61 as shown in FIG. At this time, if the block consisting of pixels x0 to x3 is the block to be smoothed, the threshold value judgment circuit 101
The following formula,

(Equation 6) By calculating, the block activity D of this block Find the ACT. Here, M in the equation (6) is an average value of the pixels x0 to x3 as shown in FIG.

The threshold decision circuit 101 determines the block activity D ACT is a predetermined threshold D Compare with TH. The threshold determination circuit 101 is a block activity D.
ACT is threshold D If it is equal to or higher than TH, the smoothing circuit 100
A comparison result signal S2 indicating that the smoothing process is to be stopped is sent. On the other hand, the threshold value judgment circuit 101
Block activity D ACT is threshold D When it is less than TH, the comparison result signal S2 indicating to execute the smoothing process is sent to the smoothing process circuit 100.

The smoothing circuit 100 includes a threshold value judging circuit 101.
When the comparison result signal S2 for executing the smoothing process is given from,

(Equation 7)

(Equation 8)

[Equation 9]

[Equation 10] The smoothed data X0 to X3 is generated by executing.

Here, AVE (•) represents an averaging processing function with threshold judgment. As an example of the averaging processing function AVE (•), for example, when the smoothed data X0 is obtained, each pixel x0, y0, y1, y11 is expressed by the following equation with respect to a predetermined threshold L:

[Equation 11] And

(Equation 12) And

(Equation 13) When there is a relationship of

[Equation 14] What is calculated based on is used. In the case of the embodiment, the comparison judgment of the relationship between the respective pixels x0, y0, y1, y11 and the threshold L is executed by the threshold judgment circuit 102, and the smoothing circuit 100 judges the threshold judgment. Based on the comparison result signal S3 of the circuit 102, the pixel used for the averaging operation is selected.

Thus, in the post-processing circuits 70 to 73, the smoothed data D71 to D based on the peripheral data in the space of the upper hierarchy.
When 74 is generated, the average calculation is not simply performed, but pixel selection is performed on the peripheral data in the space of the upper hierarchy by threshold determination. As a result, in the image decoding apparatus 60, even if an edge or the like exists near the non-divided block, the image quality deterioration due to the average calculation can be effectively avoided and the pseudo contour between the blocks can be removed.

(4) Operation of the Embodiment In the above configuration, the image decoding apparatus 60 sets the outputs of the decoders 61 to 64 to 0 for the non-division block based on the received division determination flag. At the same time, the upper layer data is output from the adders 66 to 69 to replace the non-divided block data with the upper layer data.

However, in the decoded image of this non-divided block data, a pseudo contour may occur due to the hierarchical data generation method shown in FIG. For example, in an image such as the sky where the level change is small, each block is often subjected to non-division determination. That is, it is often replaced with upper layer data. At this time, in the restored image, even if the level difference between adjacent blocks is small, a pseudo contour is often recognized at the block boundary position, which causes a large image quality deterioration.

In the hierarchical coding of the embodiment, the compression rate can be improved by setting a larger division threshold on the hierarchical coding device 40 side. However, on the side of the image decoding device 60, as the division threshold on the side of the hierarchical encoding device 40 is larger, the level difference between adjacent blocks (that is, between the divided blocks and the non-divided blocks) becomes larger, and the image quality deterioration becomes remarkable. In order to avoid this, in the image decoding device 60, the post-processing circuits 70 to 73 perform smoothing processing on the restored hierarchical data D61 to D64.
Suppress pseudo contours at block boundaries.

At this time, the post-processing circuits 70 to 73 select the smoothing processing by comparing the intra-block activity and the inter-block difference at the block boundary with a predetermined threshold value. As a result, the image decoding apparatus 60 can store important pixel information such as edges. Thus, in the image decoding apparatus 60, the pseudo contour generated between the divided block and the non-divided block can be effectively avoided, and thus the image quality deterioration can be reduced. Also, the image decoding device 60
In the above, even if a large division threshold is set on the hierarchical encoding device 40 side, the image quality deterioration can be reduced by performing the smoothing process. Therefore, a large value can be used as the division threshold in the hierarchical encoding device 40, and the compression efficiency can be further improved.

Thus, by using the image decoding device 60, it is possible to restore the image data with good compression efficiency, which is divided into blocks by the hierarchical encoding device 40 based on the block activity, in a state in which the image quality deterioration is suppressed.

(5) Effects of the Embodiments According to the above configuration, the decoded hierarchical data D61 to D61.
By providing the processing circuits 70 to 73 for smoothing 64, the pseudo contour at the block boundary can be suppressed. Also, the activity D in the block By comparing the difference between blocks at the ACT and the block boundary with a predetermined threshold value and selecting the smoothing processing according to the comparison result,
Pseudo contours can be effectively suppressed while preserving important pixels. As a result, the restored image data D55 and D71 to D74 with little image quality deterioration can be obtained from the compression-coded data D51 to D55 that are adaptively divided and have high compression efficiency.

(6) Other Embodiments In the above-described embodiments, the image data decoding method according to the present invention is divided by the independence determination method in which the threshold value is determined for each layer independently every time and division processing is performed. Although the case where the present invention is applied when decoding the compression encoded data D51 to D55 has been described, the present invention is not limited to this, and when the division of the lower layer is once stopped due to the division determination in the upper layer, the subsequent lower layers. The same effect as in the above-described embodiment can be obtained even when applied when decoding compression-encoded data for a plurality of layers obtained by a layered encoding method that suspends layer division. Further, the present invention is not limited to this, and can be widely applied to a hierarchical coding method when a plurality of blocks having different resolutions exist in hierarchical data.

[0067]

As described above, according to the present invention, by reducing the resolution of each predetermined block in the lower layer having high resolution, the block in the upper layer having low resolution corresponding to the block is generated. In the image data decoding device that sequentially generates a plurality of layer image data having different resolutions from the lower layer and decodes the layer encoded data obtained by the image encoding device that encodes the plurality of layer image data, By providing the decoding means for decoding the hierarchically encoded data and the smoothing means for smoothing the block boundary of the hierarchically decoded data obtained by the decoding means, the pseudo contour appearing at the block boundary in the hierarchically decoded data is removed. It is possible to avoid deterioration of image quality.

Further, according to the present invention, the smoothing means includes a first level detecting means for detecting a level fluctuation in the block and a second level detecting means for detecting a level fluctuation between pixels across the blocks. Means for selecting the smoothing processing based on the detection results by the first and second level detecting means, thereby saving important data such as edge data and removing pseudo contours at block boundaries. it can.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining hierarchical data generated by a hierarchical encoding device.

FIG. 2 is a chart showing an adaptive division result in an HD standard image.

FIG. 3 is a chart showing standard deviations of signal levels of respective layers in an HD standard image.

FIG. 4 is a block diagram showing a hierarchical encoding device according to an embodiment.

FIG. 5 is a block diagram showing a hierarchical encoding encoder unit.

FIG. 6 is a schematic diagram for explaining a hierarchical structure.

FIG. 7 is a flow chart showing a hierarchical encoding process.

FIG. 8 is a block diagram showing an embodiment of an image decoding apparatus according to the present invention.

FIG. 9 is a block diagram showing a configuration of a post-processing circuit.

FIG. 10 is a schematic diagram for explaining the operation of the smoothing circuit.

FIG. 11 is a block diagram showing an image coding apparatus using a conventional pyramid coding method.

12 is a block diagram showing a conventional image decoding device for decoding compression coded data generated by the image coding device of FIG. 11. FIG.

[Explanation of symbols]

40 ... Hierarchical coding device, 60 ... Image decoding device, 7
0 to 73 ... Post-processing circuit, 100 ... Smoothing circuit, 10
1, 102 ... Threshold value judgment circuit, D51-D55 ... Compressed coded data, D60-D64 ... Hierarchical data, D71
-D74, X0-X3 ... Smoothed data, m0-m7 ...
… Peripheral data in space.

[Procedure amendment]

[Submission date] January 25, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Image data decoding method and apparatus

[Claims]

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Fields of Industrial Application Conventional Technology (FIGS. 13 and 14) Problems to be Solved by the Invention Means for Solving Problems (FIGS. 10 to 12) Actions (FIGS. 10 to 12) Working Example (1) Hierarchy Principle of Coding (FIGS. 1 to 3) (2) Hierarchical Coding Device (FIGS. 4 to 9) of Embodiment (2-1) Configuration (2-2) Division Processing (3) Image Decoding of Embodiment Apparatus (FIGS. 10 to 12) (3-1) Configuration (3-2) Smoothing processing (4) Operation of the embodiment (FIGS. 10 to 12) (5) Effect of the embodiment (FIGS. 10 and 11) (6) Other Examples Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data decoding method and apparatus, and is particularly suitable for application when decoding hierarchically encoded data.

[0003]

2. Description of the Related Art Conventionally, there is an image coding apparatus which creates image data for a plurality of layers having different resolutions from input image data and codes the image data. This type of image coding apparatus is configured to hierarchically code input image data by using a hierarchical coding method such as pyramid coding. That is, in this image encoding device, high-resolution input image data is used as first layer data, second resolution data having a lower resolution than the first layer data, and second image data.
Third layer data, which has a lower resolution than the resolution data of
... are sequentially and recursively formed, and these plural hierarchical data are combined into 1
Transmission is performed by one communication path or a transmission path that is a recording / reproducing path.

Further, in the image decoding apparatus for decoding the plurality of hierarchical data, all of the plurality of hierarchical data may be decoded, and depending on the resolution of the television monitor corresponding to each of them, any one of the hierarchical data One of them may be selected and decrypted. Thus, by decoding only the desired hierarchical data from the plurality of hierarchical data, it is possible to obtain the desired image data with the minimum required transmission data amount.

As shown in FIG. 13, in an image coding apparatus 1 which realizes, for example, four-layer coding as the hierarchical coding, thinning filters 2, 3, 4 for three stages and interpolation filters 5, 6, respectively. 7 and the reduced image data D2, D3, D4 having a sequentially lower resolution are formed by the thinning filters 2, 3, 4 of the respective stages for the input image data D1 and the reduced images are generated by the interpolation filters 5, 6, 7. Data D
2. Return D3, D4 to the resolution before reduction.

Outputs D2 to D4 of the thinning filters 2 to 4
And the outputs D5 to D7 of the respective interpolation filters 5 to 7 are input to the difference circuits 8, 9 and 10, respectively, whereby difference data D8, D9 and D10 are generated. As a result, in the image encoding device 1, the amount of hierarchical data is reduced and the signal power is reduced. Here, this difference data D8
The area of each of D10 to D10 and the reduced image data D4 is 1,
The sizes are 1/4, 1/16, and 1/64.

The difference data D8 to D10 obtained from the difference circuits 8 to 10 and the reduced image data D4 obtained from the thinning filter 4 are encoded by the encoders 11, 12, 13, and 14 and compressed. As a result, the first, second, third and fourth hierarchical data D11, D12, D13 having different resolutions from the respective encoders 11, 12, 13, 14 are applied.
And D14 are sent to the transmission line in a predetermined order.

The first to fourth hierarchical data D11 to D14 thus transmitted are decoded by the image decoding device 20 shown in FIG. That is, the first to fourth hierarchical data D11 to D14 are respectively decrypted by the decoders 21, 22, and
As a result, the fourth layer data D24 is output from the decoder 24.

The output of the decoder 23 is the fourth hierarchical data D obtained from the interpolation filter 26 in the adder circuit 29.
It is added with the interpolation data of 24, whereby the third hierarchical data D23 is restored. Similarly, the output of the decoder 22 is added to the interpolation data of the third hierarchical data D23 obtained from the interpolation filter 27 in the adder circuit 30, whereby the second hierarchical data D22 is restored. Further, the output of the decoder 21 is output by the adder circuit 31 to the interpolation filter 2
8 is added to the interpolated data of the second hierarchical data D22 to restore the first hierarchical data D21.

[0010]

However, in the image coding apparatus which realizes such a hierarchical coding method, since the input image data is divided into a plurality of hierarchical data for coding, only the hierarchical component data is inevitably obtained. The amount increases, and the compression efficiency is correspondingly reduced as compared with the high efficiency coding method that does not use the hierarchical coding. Further, when trying to improve the compression efficiency, there is a problem that image quality deterioration occurs on the decoding side.

The present invention has been made in view of the above points, and proposes an image data decoding method and apparatus capable of reducing image quality deterioration when image data is hierarchically encoded and transmitted. .

[0012]

In order to solve such a problem, according to the present invention, by reducing the resolution of each predetermined block in a lower layer having a high resolution, the block in an upper layer having a lower resolution corresponding to the block. To generate a plurality of layer image data D31 to D35 having different resolutions sequentially from the lower layer, and the layer obtained by the image encoding device 40 that encodes the plurality of layer image data D31 to D35. Encoded data D51 to D5
In the image data decoding device 60 for decoding 5, the decoding means 61 to 6 for decoding the hierarchically encoded data D51 to D55.
5 and hierarchical decoded data D obtained by the decoding means 61 to 65
Smoothing means 7 for smoothing the block boundaries 61 to D64.
0-73.

In the present invention, the smoothing means 70-
Reference numeral 73 includes a first level detecting means 101 for detecting a level fluctuation in the block, and a second level detecting means 102 for detecting a level fluctuation between pixels across the blocks. The smoothing process is selected based on the detection results S2 and S3 by the second level detecting means 101 and 102.

[0014]

The smoothing means 70 smoothes the block boundaries of the hierarchically decoded data D61 to D64 decoded by the decoding means 61 to 65.
To 73, the pseudo contours appearing at the block boundaries of the hierarchically decoded data D61 to D64 can be effectively avoided, and the image quality deterioration can be reduced.

Further, a first level detecting means 101 for detecting a level fluctuation within the block and a second level detecting means 10 for detecting a level fluctuation between pixels across the blocks.
2 and the smoothing process is selected based on the detection results S2 and S3 by the first and second level detecting means 101 and 102, thereby saving important information such as edges and blocking boundaries. The pseudo contour appearing in can be effectively avoided.

[0016]

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

(1) Principle of Hierarchical Coding FIG. 1 shows, as a whole, the principle of hierarchical coding according to the present invention in which a still image such as a high definition television signal is hierarchically coded and compressed. In this layer coding, the upper layer data is created by a simple arithmetic average of the lower layer data, the lower layer data to be transmitted is reduced, and the layer structure without increasing the information amount is realized. For decoding from the upper layer to the lower layer, the amount of information in the flat portion is reduced by adaptively controlling the division based on the activity of each block. Further, in the encoding of the differential signal performed for the lower layer, the efficiency is improved by switching the quantization characteristic for each block without additional code based on the activity of the upper layer.

That is, in the hierarchical structure of this hierarchical encoding,
First, the high-definition television signal to be input is defined as the lower layer, and the four pixels X1 to X4 in the small block of 2 lines × 2 pixels in this lower layer are expressed by the following formula

[Equation 1] The arithmetic mean represented by is taken, and its value m is taken as the value of the upper hierarchy. In this lower hierarchy,

[Equation 2] As shown in, the difference value from the upper layer is prepared for three pixels, so that the hierarchical structure is configured with the same information amount as the original four pixel data.

On the other hand, when decoding the lower layer, 3 pixels X1
~ X3 is the following formula

(Equation 3) As shown by, each difference value Δ is added to the average value m of the upper hierarchy.
Xi is added to obtain the decoded value E [Xi], and the remaining one pixel is

[Equation 4] As shown by, the decoded value E [X4] is determined by subtracting the three decoded values of the lower layer from the average value m of the upper layer. Here, E [] means a decoded value.

In this hierarchical coding, one block is divided into four in order from the upper layer to the lower layer, and accordingly, the data amount is quadrupled for each layer, but is flat. The department reduces redundancy by prohibiting this division. A flag for instructing the presence / absence of this division is prepared for each bit and block. The necessity of division in the lower layer is determined as local activity, for example, the maximum value of the difference data.

Here, as an example of hierarchical coding, HD of ITE is used.
FIG. 2 shows the adaptive division result when the standard image (Y signal) is used and five-layer coding is performed. The ratio of the number of pixels in each layer to the original number of pixels when the threshold value for the maximum difference data is changed is shown, and it can be seen that redundancy is reduced based on the spatial correlation. Although the reduction efficiency changes depending on the image, if the threshold value for the maximum difference data is changed to 1 to 6, the average reduction rate becomes 28 to 69 [%].

In practice, the resolution of the upper layer is quadrupled to form a lower layer, and at this time, by encoding the difference data from the upper layer data, the signal level width can be effectively reduced. FIG. 3 shows the case of five layers by the layer coding described above with reference to FIG. 2, but here, the layers are named from the lower layers to the first to fifth layers.

Compared to the 8-bit PCM data of the original image,
A reduction in signal level width can be seen. First with a large number of pixels
Since the ~ 4 layers are differential signals, a significant reduction can be achieved and efficiency is improved by subsequent quantization. As can be seen from the table of FIG. 3, the reduction efficiency has little dependence on the pattern, and is effective for all pictures.

By forming the upper layer with the average value of the lower layer, the error propagation is stopped in the block, and the lower layer is converted into the difference from the average value of the upper layer, so that the efficiency is also provided. You can Actually, in the upper layer coding, there is a correlation in the activities between layers at the same spatial position, and by determining the quantization characteristic of the lower layer from the quantization result of the upper layer, the receiver side can be used for dequantization. It is possible to realize an adaptive quantizer that does not need to transmit quantization information (however, except for initial values).

Practically, various HD standard images (8) are obtained by hierarchically encoding an image based on the above-described five-stage hierarchical structure and expressing it in multi-resolution, and performing adaptive division and adaptive quantization using the hierarchical structure. Bit / Y / PB / PR) is about 1 /
It can be compressed to 8. The additional code for each block prepared for adaptive division is run-length coded in each layer to improve compression efficiency. In this way, an image with sufficient image quality can be obtained in each layer, and a good image without visual deterioration can be obtained even in the final lowest layer.

(2) Hierarchical Coding Device of Embodiment (2-1) Configuration In FIG. 4, reference numeral 40 denotes a hierarchical coding device, and a hierarchical coding encoder section 40A for hierarchically coding and outputting input image data D31. It is configured by a generated information amount control unit 40B which controls so that the generated information amount in the hierarchical coding encoder unit 40A becomes a target value. The hierarchical encoding encoder unit 40A is composed of a data delay memory M1 (FIG. 5) and an encoder. Of these, the memory M1 is provided in the input stage so that the data can be delayed so that the encoding process is not executed until the optimum control value is determined by the generated information amount control unit 40B.

On the other hand, the generated information amount control unit 40B inputs the input image data D31 and sets the optimum control value S1 which is suitable for the data to be processed, and this is set to the hierarchical encoding encoder unit 4
By transmitting the data to 0A, the hierarchical coding encoder unit 40A can perform efficient coding. This is a so-called feedforward buffering configuration.

The hierarchical coding encoder section 40A has the configuration shown in FIG. 5, and in this example, it is adapted to generate the compression coded image data D51 to D55 of five layers having different resolutions.

First, the input image data D31 is input to the first difference circuit 41 and the first averaging circuit 42 via the memory M1. The first averaging circuit 42 generates the second layer data D32 by averaging four pixels of the input image data D31 (that is, the first layer data (the lowest layer data)). In the case of this embodiment, the first averaging circuit 42 inputs the input image data D3 as shown in FIGS. 6D and 6E.
The four pixels X1 (1) to X4 (1) of 1 generate the pixel X1 (2) of the second hierarchical data D2.

Further, the pixel X1 of the second hierarchical data D32
Pixels X2 (2) to X4 (2) adjacent to (2) are similarly generated by obtaining the 4-pixel average of the first layer data D31. The second layer data D32 is the second difference circuit 4
3 and the second averaging circuit 44, and the second averaging circuit 44 generates the third hierarchical data D33 by averaging four pixels of the second hierarchical data D32. For example, FIG. 6 (C)
And pixel D1 of the second hierarchical data D32 shown in (D)
(2) to X4 (2) to the pixel X of the third hierarchical data D33
1 (3) is generated, and pixels X2 (3) to X4 (3) adjacent to the pixel X1 (3) are also generated by the four pixels of the second hierarchical data D32.

The third layer data D33 is the third difference circuit 4
5 and the third averaging circuit 46, and the third averaging circuit 46 uses the four-pixel average of the third hierarchical data D33 as shown in FIGS. 6B and 6C, as in the case described above. ,
Fourth layer data D3 including pixels X1 (4) to X4 (4)
4 is generated. The fourth layer data D44 is input to the fourth difference circuit 47 and the fourth averaging circuit 48, and the fourth averaging circuit 48 becomes the uppermost layer by the 4-pixel average of the fourth layer data D34. Hierarchical data D35 is generated.
That is, as shown in FIGS. 6A and 6B, the pixels X1 (5) of the fifth layer data D35 are averaged by averaging the four pixels X1 (4) to X4 (4) of the fourth layer data D34.
Is generated.

Here, the first to fifth hierarchical data D31 to D3
As for the block size of 5, when the block size of the first layer data D31 which is the lowest layer is 1 line × 1 pixel, the second layer data D32 is 1/2 line × 1/2 pixel, and the third layer data D33 is 1/4 line × 1/4 pixel, the fourth layer data D34 is 1/8 line × 1/8 pixel, and the fifth layer data D35 which is the highest layer data is 1
/ 16 line × 1/16 pixel.

The hierarchical coding encoder section 40A repeats the recursive processing in order from the highest hierarchical data (that is, the fifth hierarchical data D35) among the first to fifth hierarchical data D31 to D35 and the two adjacent data. The difference between the hierarchical data is obtained by the difference circuits 41, 43, 45 and 47,
Only the difference data is compression-encoded by the encoders 51-55. As a result, the hierarchical encoding encoder unit 40A compresses the amount of information transmitted on the transmission path.
In addition, the hierarchical encoding encoder 40A uses the encoders 51 to 54, as described above with respect to the expression (2), to determine the upper layer 1
The transmission data is reduced by reducing one pixel among the lower four pixels corresponding to the pixel. In order to keep such a compression condition optimum, the hierarchical coding encoder unit 40A decodes the compressed coded data D51 to D55 obtained for each hierarchical layer by the decoders 56 to 59.

That is, the decoder 5 corresponding to the highest layer
Reference numeral 9 restores the compression-encoded data D55 compression-encoded by the encoder 55 to obtain decoded data D48 corresponding to the fifth layer data D35, and supplies this to the fourth difference circuit 47.

On the other hand, the decoder 58 decompresses the compression coded data D54 to obtain decompressed data D47 similar to the fourth layer data D44, and supplies this to the third difference circuit 45. Similarly, the decoder 57 restores the compression encoded data D53 and restores the restored data D4 similar to the third layer data D43.
6 is given to the second difference circuit 43. Also, the decoder 56 restores the compression encoded data D52 to obtain the restored data D45 similar to the second layer data D42,
To the difference circuit 41.

In practice, the decoders 58, 57, 56 are shown in FIG.
It is configured as shown in FIG. Here, the decoder 58 will be described for simplification. The decoder 58 is the decoding circuit 5
8A receives the fourth layer compression encoded data D54 and decodes it. As a result, the decoding circuit 58A outputs, for example, X1 (4) -X1 (5) and X2 (4) -X1 shown in FIG.
Output values of (5) and X3 (4) -X1 (5) are obtained.
This output value is reconstructed by the reconstructed data D in the addition circuit 58B.
By adding 48, X1 (4), X2 (4),
It is obtained from the output value of X3 (4). Difference value generation circuit 58
C is X1 (4), X2 (4), X3 (4) and X1
Non-transmission pixel X4 (4) is generated by performing an operation based on equation (4) using (5). Therefore, from the subsequent synthesizing circuit 58D, the fourth hierarchical data X1 (4) before the difference,
X2 (4), X3 (4), and X4 (4) are generated and given to the difference circuit 45.

The inter-layer difference data D41 to D44 obtained by the difference circuits 41, 43, 45 and 47 are compression-encoded by the encoders 51 to 54, respectively. At this time, the encoders 51 to 54 compare the activity of each block with a predetermined threshold value. Here, the activity is the difference data D41 to D between the layers when the lower layer data area corresponding to the upper layer data is defined as "block".
Maximum error within block, average error within block, sum of absolute values within block, standard deviation within block of 44 predetermined blocks,
It is a correlation value that represents the sum of n powers in a block or the data frequency above a threshold value in a block. That is, when the activity is low, this block can be called a flat block.

At this time, if the block activity is higher than a predetermined threshold, the encoders 51 to 54 select this block as a divided block and select a division process in an adjacent lower hierarchical block spatially corresponding to the block. To do.
For example, for a block for which division processing is selected by the encoder 54, the following encoder 53 compression-codes the inter-layer difference data D43 corresponding to this block as it is, and at the same time, a division determination flag indicating that this block is a division block. Attach and transmit.

On the other hand, if the block activity is less than the predetermined value, the encoders 51 to 54 regard this block as a non-divided block and stop the division process in the adjacent lower hierarchical block spatially corresponding to the block. To do. For example, with respect to a block determined to be discontinued by the encoder 54, the subsequent encoder 53 excludes the inter-layer difference data D43 corresponding to this block from the encoding target, and at the same time, this block is a non-divided block. Is transmitted with a non-division determination flag indicating. This non-divided block is replaced with upper layer data on the decoding device side.

Here, the encoders 51, 52, 53 and 54 are constructed as shown in FIG. FIG. 8 shows the configurations of the encoders 52 and 53 for simplification. That is, the difference data D42 and D43 are encoded by the encoders 52 and 53, respectively.
Are input to the encoding circuits 52A and 53A. Further, the difference data D42 and D43 are respectively divided control units 52B and 5B.
It is input to the activity detection circuits 52C and 53C of 3B. The activity detection circuits 52C and 53C detect the activity of each of the predetermined blocks of the difference data D42 and D43, and apply the detection results obtained thereby to the subsequent threshold value determination circuits 52D and 53D. Threshold value judgment circuit 52
D and 53D compare the activity detection result for each block with the threshold value data D57 from the generated information amount control unit 40B, and the determination result obtained by this is encoded circuit 52A,
Send to 53A. The coding circuits 52A and 53A compress and code the blocks with high activity on the basis of the result of the threshold value judgment, and transmit the blocks with low activity, on the other hand.

(2-2) Division Processing Next, concrete signal processing by the hierarchical encoding encoder section 40A will be described. In the hierarchical encoding encoder unit 40A, as described above, the inter-layer difference data D41 to D44.
The division selection processing is executed based on the block activity for each predetermined block. In the case of the embodiment, each block is composed of 2 lines × 2 pixels.

Here, the data value of each pixel is X, and the hierarchy of the data value X is represented by a suffix. That is, when the upper layer data is Xi + 1 (0), the adjacent lower layer data can be represented as Xi (j) (j = 0 to 3). Therefore, the inter-tier difference data value ΔXi (j) is

(Equation 5) Can be represented by

The encoders 51 to 54 compare the block activity and the threshold value for each block, and select whether to divide this block in the lower hierarchy or not to divide it based on the comparison result. That is, in the encoders 51 to 54, the division in the lower layer is executed when the block activity is equal to or more than the threshold, whereas the division in the lower layer is stopped when the block activity is less than the threshold.

As a result, the hierarchical coding device 40 does not have to send the data of the adjacent lower layer corresponding to this block for a block having a low block activity, and the transmission information amount can be reduced accordingly. Incidentally, a 1-bit judgment flag is used as the judgment flag indicating the judgment result of division or non-division.

The threshold value used in the block activity determination by each of the encoders 51 to 54 is the generated information amount control unit 4
It is set according to the optimum control value S1 sent from 0B. That is, as the threshold value increases, the number of non-divided blocks (non-transmission block) increases, and the amount of transmission information decreases. In this way, the hierarchical encoding encoder unit 40
In A, compression coding is performed in order from the upper layer data having a lower resolution, and at this time, the activity is determined for each predetermined block of each layer data, and the block having the lower activity corresponds to this block in the adjacent lower layer. It is designed not to send image data to be used.

Further, in the hierarchical coding system in the embodiment,
A method is used in which the judgment flag is not reflected in the judgment in the subsequent lower layers (hereinafter referred to as an independent judgment method). That is, in the independence determination method, division selection processing based on the threshold value determination is performed every time for each layer independently. For example, even for a block for which non-division determination has been performed once, the activity determination is performed again in the subsequent lower layer, and it is selected here whether to divide again or not. As a result, in the hierarchical coding method using the independent judgment method, the hierarchical coding with less image quality deterioration can be realized without being affected by the judgment flag of the lower hierarchy in the upper hierarchy.

Here, FIG. 9 shows a flow chart of the hierarchical coding processing by the hierarchical coding device 40, and step SP
"4" in the hierarchy counter 1 which stores the hierarchy number in 2
Is registered, and the frame of this hierarchical coding is determined.

Further, in step SP3, the generated information amount control section 40B calculates the generated information amount to generate hierarchical data, and in the following step SP4, each block activity is detected. Generated information amount control unit 40
B determines the optimum control value S1 in step SP5 based on this activity.

Further, in step SP6, the hierarchical coding encoder section 40A executes hierarchical coding based on the optimum control value S1. That is, 5 which is the highest layer at the beginning
Encoding and decoding are performed on the hierarchical data. This result becomes the initial value of the processing in the lower layer, and the difference value between layers with the lower layer is generated in step SP7. Further, in step SP8, division selection and encoding in the lower hierarchy are executed based on the optimum control value S1 determined in step SP5.

After each layer processing, the layer counter I is decremented in step SP9. And step S
In P10, the end determination is performed on the contents of the hierarchy counter 1. If not completed, the lower layer processing is continued. When the processing of all layers is completed, the loop is exited and the layer encoding processing is completed in step SP11.

(3) Image Decoding Device of the Embodiment (3-1) Configuration The first to fifth signals thus transmitted together with the division determination flag.
The compression coded data D51 to D55 of the layers are decoded by the image decoding device 60 as shown in FIG. That is, the first to fifth layer compression encoded data D51 to D55
Are decoders 61, 62, 6 having a decoding method reverse to that of the encoders 57, 55, 53, 51 and 49, respectively.
3, 64 and 65 are input. As a result, the decoders 61 to 61
The inter-tier difference data D56 to D59 of the first to fourth hierarchies respectively decoded by 64 are input to the first to fourth adder circuits 66 to 69, respectively.

The fifth layer compression coded data D55 is decoded by the decoder 65, and the resulting fifth layer data D60 is output as it is and the fourth addition circuit 6 is also provided.
9 is sent. The fourth adding circuit 69 adds the fifth layer data D60 and the fourth layer inter-layer difference data D59 to restore the fourth layer data D64, and sends this to the fourth post-processing circuit 73 and at the same time. 3 to the adder circuit 68.

Similarly, the third addition circuit 68 adds the fourth layer data D64 and the third layer difference data D58 to restore the third layer data D63, which is then added to the third post-processing circuit. It is sent to the second addition circuit 67 as well as to the second addition circuit 67. Similarly, the second and first adding circuits 67
And 66, the second layer data D62 and the first layer data D61 are restored, and these are sent to the second and first post-processing circuits 71 and 70, respectively.

The first to fourth post-processing circuits 70 to 73 examine the contents of the hierarchical data D61 to D64, respectively, and adaptively perform smoothing processing so that pseudo contours at block boundaries are obtained. It is designed to be removed. That is, since the hierarchical encoding device 40 described above introduces the inter-layer block division processing, a pseudo contour may occur along the block boundary depending on the threshold value used in the block division. Therefore, the first to fourth post-processing circuits 70-
73 effectively removes the pseudo contour generated on the decoding side by the smoothing process to smooth the smoothed data D71 to D71.
Generate D74.

(3-2) Smoothing processing Here, the post-processing circuits 70 to 73 are configured as shown in FIG. Since the post-processing circuits 70 to 73 have the same configuration, the post-processing circuit 70 will be described below. The post-processing circuit 70 inputs the first layer data D61 output from the addition circuit 66 to the smoothing circuit 100 and the threshold value determination circuits 101 and 102.

The threshold value judgment circuit 101 uses the first layer data D
The intra-block data fluctuation of 61 (that is, intra-block activity) is obtained, this is compared with a predetermined threshold value, and the comparison result is sent to the smoothing circuit 100 as a comparison result signal S2. Further, the threshold determination circuit 102 obtains a block-to-block data difference at the block boundary of the first layer data D61, compares this with a predetermined threshold, and sends the comparison result to the smoothing circuit 100 as a comparison result signal S3. The smoothing circuit 100 selects pixels to be smoothed based on the comparison result signals S2 and S3.

Practically, the post-processing circuit 70 inputs the first layer data D61 as shown in FIG. At this time, for example, if the block consisting of pixels x0 to x3 is the block to be smoothed, the threshold value judgment circuit 101
The following formula,

(Equation 6) The block activity D_ACT of this block is obtained by calculating Here, M in the equation (6) is an average value of the pixels x0 to x3 as shown in FIG.

The threshold decision circuit 101 compares this block activity D_ACT with a predetermined threshold D_TH. The threshold determination circuit 101 is a block activity D.
If _ACT is greater than or equal to the threshold value D_TH, the smoothing circuit 100
A comparison result signal S2 indicating that the smoothing process is to be stopped is sent. On the other hand, the threshold value judgment circuit 101
When the block activity D_ACT is less than the threshold value D_TH, the comparison result signal S2 indicating that the smoothing process is executed is sent to the smoothing process circuit 100.

The smoothing circuit 100 includes a threshold value judging circuit 101.
When the comparison result signal S2 for executing the smoothing process is given from,

(Equation 7)

(Equation 8)

[Equation 9]

[Equation 10] The smoothed data X0 to X3 is generated by executing.

Here, AVE (•) represents an averaging processing function with threshold value judgment. As an example of the averaging processing function AVE (•), for example, when the smoothed data X0 is obtained, each pixel x0, y0, y1, y11 with respect to a predetermined threshold L, the following equation,

[Equation 11] And

(Equation 12) And

(Equation 13) When there is a relationship of

[Equation 14] What is calculated based on is used. In the case of the embodiment, the comparison judgment between the relationship between the pixels x0, y0, y1, y11 and the threshold value L is executed by the threshold value judgment circuit 102, and the smoothing circuit 100 makes the threshold value judgment. Based on the comparison result signal S3 of the circuit 102, the pixel used for the averaging operation is selected.

Thus, in the post-processing circuits 70 to 73, the smoothed data D71 to D based on the peripheral data in the space of the upper hierarchy.
When 74 is generated, the average calculation is not simply performed, but pixel selection is performed on the peripheral data in the space of the upper hierarchy by threshold determination. As a result, in the image decoding apparatus 60, even if an edge or the like exists near the non-divided block, the image quality deterioration due to the average calculation can be effectively avoided and the pseudo contour between the blocks can be removed.

(4) Operation of the Embodiment In the above configuration, the image decoding device 60 sets the outputs of the decoders 61 to 64 to 0 for the non-division block based on the received division determination flag. At the same time, the upper layer data is output from the adders 66 to 69 to replace the non-divided block data with the upper layer data.

However, in the decoded image of this non-divided block data, a pseudo contour may occur due to the hierarchical data generation method shown in FIG. For example, in an image such as the sky where the level change is small, each block is often subjected to non-division determination. That is, it is often replaced with upper layer data. At this time, in the restored image, even if the level difference between adjacent blocks is small, a pseudo contour is often recognized at the block boundary position, which causes a large image quality deterioration.

In the hierarchical coding of the embodiment, the compression rate can be improved by setting a larger division threshold on the hierarchical coding device 40 side. However, on the side of the image decoding device 60, as the division threshold on the side of the hierarchical encoding device 40 is larger, the level difference between adjacent blocks (that is, between the divided blocks and the non-divided blocks) becomes larger, and the image quality deterioration becomes remarkable. In order to avoid this, in the image decoding device 60, the post-processing circuits 70 to 73 perform smoothing processing on the restored hierarchical data D61 to D64.
Suppress pseudo contours at block boundaries.

At this time, the post-processing circuits 70 to 73 select the smoothing process by comparing the intra-block activity and the inter-block difference at the block boundary with a predetermined threshold value. As a result, the image decoding apparatus 60 can store important pixel information such as edges. Thus, in the image decoding apparatus 60, the pseudo contour generated between the divided block and the non-divided block can be effectively avoided, and thus the image quality deterioration can be reduced. Also, the image decoding device 60
In the above, even if a large division threshold is set on the hierarchical encoding device 40 side, the image quality deterioration can be reduced by performing the smoothing process. Therefore, a large value can be used as the division threshold in the hierarchical encoding device 40, and the compression efficiency can be further improved.

Thus, by using the image decoding device 60, it is possible to restore the image data with good compression efficiency which is block-divided by the hierarchical encoding device 40 based on the block activity, while suppressing the image quality deterioration.

(5) Effects of the Embodiments According to the above configuration, the decoded hierarchical data D61 to D61.
By providing the post-processing circuits 70 to 73 for smoothing 64, the pseudo contour at the block boundary can be suppressed. Also, by comparing the intra-block activity D_ACT and the inter-block difference at the block boundary with a predetermined threshold value and selecting the smoothing process according to the comparison result, the pseudo contour is effective while preserving important pixels. Can be suppressed to. As a result, the restored image data D55 and D71 to D74 with little image quality deterioration can be obtained from the compression-coded data D51 to D55 that are adaptively divided and have high compression efficiency.

(6) Other Embodiments In the above-described embodiments, the image data decoding method according to the present invention is divided by the independence determination method in which the threshold value determination is performed for each layer independently each time and the division processing is performed. Although the case where the present invention is applied when decoding the compression encoded data D51 to D55 has been described, the present invention is not limited to this, and when the division of the lower layer is once stopped due to the division determination in the upper layer, the subsequent lower layers. The same effect as in the above-described embodiment can be obtained even when applied when decoding compression-encoded data for a plurality of layers obtained by a layered encoding method that suspends layer division. Further, the present invention is not limited to this, and can be widely applied to a hierarchical coding method when a plurality of blocks having different resolutions exist in hierarchical data.

[0069]

As described above, according to the present invention, by reducing the resolution of each predetermined block in the lower layer having high resolution, the block in the upper layer having low resolution corresponding to the block is generated. In the image data decoding device that sequentially generates a plurality of layer image data having different resolutions from the lower layer and decodes the layer encoded data obtained by the image encoding device that encodes the plurality of layer image data, By providing the decoding means for decoding the hierarchically encoded data and the smoothing means for smoothing the block boundary of the hierarchically decoded data obtained by the decoding means, the pseudo contour appearing at the block boundary in the hierarchically decoded data is removed. It is possible to avoid deterioration of image quality.

Further, according to the present invention, the smoothing means includes the first level detecting means for detecting the level fluctuation in the block and the second level detecting means for detecting the level fluctuation between the pixels across the blocks. Means for selecting the smoothing processing based on the detection results by the first and second level detecting means, thereby saving important data such as edge data and removing pseudo contours at block boundaries. it can.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining hierarchical data generated by a hierarchical encoding device.

FIG. 2 is a chart showing an adaptive division result in an HD standard image.

FIG. 3 is a chart showing standard deviations of signal levels of respective layers in an HD standard image.

FIG. 4 is a block diagram showing a hierarchical encoding device according to an embodiment.

FIG. 5 is a block diagram showing a hierarchical encoding encoder unit.

FIG. 6 is a schematic diagram for explaining a hierarchical structure.

FIG. 7 is a block diagram showing the configuration of a decoder.

FIG. 8 is a block diagram showing a configuration of an encoder.

FIG. 9 is a flow chart showing a hierarchical encoding process.

FIG. 10 is a block diagram showing an embodiment of an image decoding apparatus according to the present invention.

FIG. 11 is a block diagram showing a configuration of a post-processing unit.

FIG. 12 is a schematic diagram for explaining the operation of the smoothing circuit.

FIG. 13 is a block diagram showing an image coding apparatus using a conventional pyramid coding method.

FIG. 14 is a block diagram showing a conventional image decoding device for decoding the compression encoded data generated by the image encoding device of FIG.

[Description of Codes] 40 ... Hierarchical coding device, 60 ... Image decoding device, 7
0 to 73 ... Post-processing circuit, 100 ... Smoothing circuit, 10
1, 102 ... Threshold value judgment circuit, D51-D55 ... Compressed coded data, D60-D64 ... Hierarchical data, D71
-D74, X0-X3 ... Smoothed data, m0-m7 ...
… Peripheral data in space.

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Claims (9)

[Claims] 1. A block in an upper layer having a lower resolution corresponding to the block is generated by reducing the resolution of each predetermined block in a lower layer having a higher resolution, and the resolutions are sequentially changed from the lower layer. In an image data decoding method for generating a plurality of layered image data and decoding the layered encoded data obtained by an image encoding device that encodes the plurality of layered image data, by decoding the layered encoded data, An image data decoding method, characterized in that hierarchical decoded data is generated and a block boundary of the hierarchical decoded data is smoothed. 2. The image data decoding according to claim 1, wherein a level variation in the block of the hierarchically decoded data is detected, and the smoothing process is performed on a block boundary of the block having a small level variation. Method. 3. The image according to claim 1, wherein a level change between pixels in the block of the hierarchical decoded data is detected, and the smoothing process is performed on a pixel having a small level change. Data decryption method. 4. A level variation within the block of the hierarchical decoded data is detected, and a level variation between pixels in the block of the hierarchical decoded data is detected. 2. The image data according to claim 1, wherein the block boundary of blocks less than a threshold value is subjected to the smoothing processing using pixels whose level variation between pixels across the blocks is less than a predetermined threshold value. Decryption method. 5. The resolution is sequentially reduced from the lower layer by reducing the resolution of each predetermined block of the lower layer having the higher resolution to generate a block in the upper layer having a lower resolution corresponding to the block. An image data decoding apparatus for generating a plurality of layer image data and decoding the layer encoded data obtained by an image encoding apparatus for encoding the plurality of layer image data, the decoding means for decoding the layer encoded data. And a smoothing means for smoothing a block boundary of the hierarchically decoded data obtained by the decoding means. 6. The smoothing means comprises level detection means for detecting level fluctuations in the block, and smooths a block boundary of the block when the level fluctuations in the block is less than a predetermined threshold value. The image data decoding device according to claim 5, wherein 7. The smoothing means comprises level detecting means for detecting a level variation between pixels across the blocks, and smoothes pixels whose level variation is less than a predetermined threshold value. The image data decoding device according to claim 5. 8. The smoothing means includes a first level detecting means for detecting a level fluctuation in the block, and a second level detecting means for detecting a level fluctuation between pixels across the blocks. 6. The smoothing process is selected based on the detection results of the first and second level detecting means.
The image data decoding device according to 1. 9. A block boundary of blocks whose level detection result by said first level detecting means is less than a predetermined threshold value is smoothed by using pixels whose level detection result by said second level detecting means is less than a predetermined threshold value. The image data decoding device according to claim 5, wherein the image data decoding process is performed.