JP3221120B2 - Decryption device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a decoding apparatus which is applied to a receiving side when an image signal is coded according to a dynamic range.

[0002]

2. Description of the Related Art The present applicant has disclosed in Japanese Patent Application Laid-Open No.
High-efficiency coding for obtaining a dynamic range defined by a maximum value and a minimum value of a plurality of pixels included in a two-dimensional block and performing encoding adapted to the dynamic range as described in the specification of Japanese Patent No. The device is proposed.

Further, as described in Japanese Patent Application Laid-Open No. 62-92620, a highly efficient three-dimensional block formed from pixels in an area included in each of a plurality of frames is adapted to be adapted to a dynamic range. An encoding device has been proposed.

Further, as described in Japanese Patent Application Laid-Open No. Sho 62-128621, there has been proposed a variable length coding method in which the number of bits changes according to a dynamic range in which the maximum distortion is constant. . Further, Japanese Patent Application Laid-Open
As described in the specification of Japanese Patent No. 111781, there has been proposed a feedforward type buffering device which uses an integrated frequency distribution table.

[0005] Coding adapted to these dynamic ranges (abbreviated as ADRC) has little deterioration in image quality,
It is also efficient. On the decoding side of ADRC,
When the number of quantization bits is n, the median of the level range having a quantization step width obtained by dividing the dynamic range into 2 ⁿ pieces is output as the decoding level.

As in the prior art, when the median value is used as the restoration level, there is a problem that when the number of quantization bits of the ADRC is small, the quantization distortion increases. Therefore, a decoding device capable of reducing quantization distortion when decoding an encoded code obtained by ADRC has been proposed by the applicant of the present application (Japanese Patent Application Laid-Open Nos. 1-200883 and 1). -200884, JP-A-1-200885). According to the invention described in this specification, quantization distortion is reduced by adaptively taking the most probable value determined from the situation around the target pixel.

[0007] The previously proposed decoding will be described with reference to FIGS. 7 and 8. Regarding the received code and the corresponding coded code DT, a plurality of, for example, 8
The encoded codes of the peripheral pixels are extracted. That is, in FIG. 8A, the encoded code X0 of the target pixel indicated by black dots and the encoded codes X1 to X8 of eight peripheral pixels around the target pixel are extracted.

The magnitude relationship between each of the encoded codes X1 to X8 of the peripheral pixels and the encoded code X0 of the target pixel is detected. The coded code X0 of the pixel of interest is compared with the coded codes Xi (i = 1, 2,... 8) of the peripheral pixels,
The following comparison output is formed:

When Xi> X0: +1 When Xi = X0: 0 When Xi <X0: −1

[0010] The comparison outputs are totaled. For example, FIG.
As shown in (2), when the encoded code X0 is 2 (= (10)) and X1 to X8 are all 1 (= (01)), the total value is -8. Further, as shown in FIG. 8C, the encoded code X0 is 2 (= (10)) and X1 to X8 are all 3 (= (1
In the case of 1)), the total value is +8. That is, the total value is 17 values (−8 to +8). However, X0
Is 3 (= (11)), the distribution of tally values is (0−−).
8), and when X0 is 0 (= (00)), there are nine distributions of total values (0 to +8). Therefore, the total value can take 52 values in all according to the encoding code X0 of the target pixel.

[0011] Division of averaging to reduce the total value to 1/8 and c ×
A correction code c is formed by multiplication (normalization) of 0.5, and this correction code is added to the encoded code X0.
The coded code X0 'after the correction of (X0' = X0 + c) is subjected to a decoding process, and a restoration level corresponding to X0 'is formed. This restoration level is added to the minimum value MIN. As compared with the conventional method in which the median value is set as the decoding level, the restoration level of the target pixel having a more subdivided level can be obtained.

FIG. 7 is a flowchart of the above-described decoding process. In the initial setting step 41, (c = 0,
i = 0). In the next step 42, it is determined whether or not Xi> X0 holds. If this holds, c = c + 1 (step 43), and the control moves to the next step 44. In step 44, it is determined whether Xi <X0 is satisfied. If this holds,
c = c-1 (step 45), and the next step 46
The control moves to.

In step 46, it is determined whether or not i ≦ 8. When the condition is satisfied, the process returns to step 42 via step 47 in which i = i + 1. That is, X1
The above processing is repeated for .about.X8. When the processing of these peripheral coded codes is completed, in step 48, averaging processing of c / 8 is performed. And c ×
A correction code is formed by the normalization step 49 for performing the processing of 0.5, and this correction code is added to the encoded code X0 of the target pixel (step 55). This normalization prevents encoded data from changing when dubbing results in re-encoding the decoded result.

[0014]

The above-described decoding apparatus uniformly performs correction according to the magnitude relationship between the encoded data around the encoded data and the encoded data of the pixel of interest. As a result, in a block having a large dynamic range, such as an edge block, a correction value to be added to an encoded code becomes large, and there is a problem that an edge portion is rounded.

Accordingly, an object of the present invention is to provide a decoding device in which the edge portion is prevented from being rounded by using a normalized correction value without uniformly adding a correction code. It is in.

[0016]

According to a first aspect of the present invention, input data is divided into blocks each including a plurality of pixels, and each pixel is adapted to dynamic range information obtained from a maximum value and a minimum value for each block. The information is encoded with a smaller number of bits than the original quantized bit number, and the encoded data and additional information for each block including at least two of the maximum value, the minimum value, and data relating to the dynamic range information are transmitted. A decoding device that decodes the encoded data based on the transmission data, the information comparing the encoded data of the pixel of interest to be decoded and the information associated with the encoded data of a plurality of peripheral pixels with each other. Circuit, a correction value generation circuit for generating a correction value based on an output of the comparison circuit, and a correction range of an output of the correction value generation circuit for a dynamic range of a block of a target pixel. A circuit for normalizing the function, a decoding device including a circuit for generating the decoded data based on the output of the encoded data, the additional information and normalization circuit of the pixel of interest.

According to a second aspect of the present invention, in the decoding device of the first aspect, the normalization circuit normalizes the correction value of the output of the correction value generation circuit by a function of the dynamic range of the block of the pixel of interest, and Control is performed so that adaptive decoding using a correction value is not performed in a small block.

[0018]

The image signal has a local correlation. That is, the level of the pixel of interest to be decoded has a correlation with the levels of peripheral pixels. Therefore, since the encoded code of the target pixel and the encoded codes of the peripheral pixels have a correlation, a decoding step that is more detailed than the original decoding level step is performed in accordance with the level relationship between the two. This can be realized by a normalized correction code. Since the dynamic range DR of the block including the edge portion becomes large, normalization is performed using a function of the dynamic range DR. Therefore, the value added to the encoded code is
When the dynamic range is large, the dynamic range becomes small, and it is possible to prevent the edge portion of the decoded image from dulling.

[0019]

An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, on the transmission side, a video signal is converted into a two-dimensional block structure, and a variable number of bits n (n = 0, n = 0,
ADRC that quantizes to 1, 2, 3 or 4 bits). For easy understanding, the transmitting side will be described with reference to FIG.

In FIG. 1, a digital video signal is supplied to an input terminal indicated by 1. This digital video signal is supplied to the blocking circuit 2, which converts the television scanning order into the block order. As shown in FIG. 2, one block includes (x pixels ×
(y-line). The output signal of the blocking circuit 2 is supplied to a maximum value detection circuit 3 for detecting the maximum value MAX for each block, a minimum value detection circuit 4 for detecting the minimum value MIN for each block, and a delay circuit 5.

The detected maximum value MAX and minimum value MIN
Is supplied to the subtraction circuit 6, and the maximum value MAX and the minimum value MIN
Is obtained from the subtraction circuit 6. The delay circuit 5 has a maximum value MAX and a minimum value MIN.
Delay the data by the time required to detect The minimum value MIN is subtracted from the video data from the delay circuit 5 in the subtraction circuit 7, and the data PDI after the minimum value is removed is obtained from the subtraction circuit 7.

The data PDI after the removal of the minimum value is
Is supplied to the quantization circuit 9 via the. The quantization circuit 9 includes a dynamic range DR from the delay circuit 10 and threshold values T1, T2, and T from the buffering circuit 11.
3, T4 are supplied. In the quantization circuit 9, the number n of bits allocated to the block is determined from the dynamic range DR of the block and the thresholds T1 to T4, and a code signal DT is generated by requantization using the number n of allocated bits.

In the buffering circuit 11, a frequency distribution table for a predetermined period of the dynamic range DR, for example, one frame period is formed, and then this frequency distribution table is converted into an integrated frequency distribution table. Against ROM
The threshold value sets T1 to T4 (T1 <T2 <T3 <T4) from the threshold value table stored in 12 are applied, and the amount of data generated for each of the plurality of threshold value sets is calculated. You. A set of thresholds is determined so that the amount of data generated during one frame period does not exceed the target value. This set of threshold values is supplied to the quantization circuit 9.

In the quantization circuit 9, the dynamic range D
R and selected thresholds T1 to T4 (T1 <T2 <T3
<T4), and the number n of allocated bits is determined based on the relationship between the dynamic range DR and the threshold values T1 to T4. The variable-length ADRC can perform efficient encoding by reducing the number of allocated bits n in a block having a small dynamic range DR and increasing the number of allocated bits n in a block having a large dynamic range DR.

That is, the block of (DR <T1)
No code signal is transmitted, only the dynamic range DR and the average value MIN are transmitted, and the block of (T1 ≦ DR <T2) is set to (n = 1), and (T2 ≦ DR <T3)
Are (n = 2), and (T3 ≦ DR <T
The block of 4) is (n = 3), and (DR ≧ T4)
Is (n = 4). Requantization is performed using the number of allocated bits n determined in this way. The quantization circuit 9 is configured by a ROM or an arithmetic circuit.

In the ROM 12, a set of thresholds (T1, T
2, T3, T4), for example, 32 sets are prepared.
A set of these threshold values is a parameter code Pi (i =
0, 1, 2, ..., 31). The amount of generated information is set to decrease monotonically as the number i of the parameter code Pi increases. However, as the amount of generated information decreases, the image quality of the restored image deteriorates.

In the quantization circuit 9, when (n = 2),
A, the dynamic range DR is (2 ² =
4) A 2-bit encoded code DT is allocated corresponding to the level range to which the divided data PDI to which the minimum value has been removed belongs. In the conventional ADRC decoding method, the median of each level range is decoded as the representative level. The encoding shown in FIG. 3A is a process represented by the following equation, where the value of the encoded code DT obtained corresponding to the original level Li is X0.

X0 = (Li−MIN) × 2 ⁿ / DR The above processing is to round down to an integer.

As a quantization method, as shown in FIG. 3B, a method in which a maximum value MAX and a minimum value MIN can be obtained as a decoding level may be used.

The dynamic range DR, the minimum value MIN,
An additional code consisting of a parameter code Pi for identifying a set of thresholds and an encoded code DT are supplied to the framing circuit 14. The framing circuit 14 performs encoding for error correction and adds a synchronization signal. Transmission data is obtained at the output terminal 15 of the framing circuit 14.

FIG. 4 shows a configuration of a receiving side (decoding) that receives and decodes the above-described transmission data. The present invention is applied to this receiving side. Data received from an input terminal indicated by reference numeral 21 is supplied to a frame decomposition circuit 22.
The frame decomposition circuit 22 decodes the error correction code, and separately obtains a parameter code Pi, a minimum value MIN, a dynamic range DR, and an encoded code DT for identifying a set of thresholds from the frame decomposition circuit 22. . The minimum value MIN and the dynamic range DR are supplied to delay circuits 23 and 24, respectively. The parameter code Pi is supplied as an address to the ROM 25 storing the threshold value table. A set of thresholds (T1, T2, T3, T4) is read from the ROM 25.

The encoded code DT is supplied to the peripheral data extracting circuit 26, and the encoded codes of a plurality of, for example, eight peripheral pixels around the pixel of interest are extracted. That is,
The peripheral data extracting circuit 26 is a circuit that simultaneously extracts the encoded code X0 of the target pixel indicated by a black dot and the encoded codes X1 to X8 of eight peripheral pixels around the target pixel in FIG. 8A. Peripheral data extraction circuit 26
Is to extract the encoded codes of the surrounding pixels at the same time,
Has memory. As the peripheral data, data of a pixel in the same block as the pixel of interest is extracted. If the pixel at the end of the block is the target pixel, the peripheral pixels are included in another block. In this case, the encoded data of the peripheral pixels are interpolated by the pixels in the same block.

Output data from the peripheral data extracting circuit 26 is supplied to a comparing circuit 27. The comparison circuit 27 includes
Eight comparators are included. Each of these comparators has
The encoded codes X1 to X8 of the peripheral pixels are supplied from the peripheral data extracting circuit 26, and the encoded code X0 of the pixel of interest is commonly supplied. Each comparator calculates the coded code X0 of the pixel of interest and the coded code Xi (i
= 1, 2, ... 8) to generate the following comparison output.

When Xj> X0: +1 When Xj = X0: 0 When Xj <X0: −1

The output signal of the comparison circuit 26 is supplied to the summing circuit 28, and the comparison output is added. For example, as shown in FIG. 8B, when the encoded code X0 is 2 (= (10)),
When all of 1 to X8 are 1 (= (01)), the counting circuit 2
The total value of 8 is -8. Also, as shown in FIG. 8C,
When the encoded code X0 is 2 (= (10)) and X1 to X8 are all 3 (= (11)), the total value of the totaling circuit 28 is +8. That is, the total value is (−8 to +8) of 17
The value is as follows. However, when X0 is 3 (= (11)), there are nine distributions of total values (0 to -8), and X0
Is 0 (= (00)), the distribution of the aggregated value is (0 ++
8) 9 cases. Therefore, the total value can take 52 values in all according to the encoding code X0 of the target pixel.

The output signal of the counting circuit 28 is supplied to a correction code generation circuit 29. The correction code generation circuit 29 divides the total value by ８ and multiplies the quotient by a value of 0.5. The correction code generation circuit 29 is constituted by, for example, a ROM. The correction code obtained at the output of the correction code generation circuit 29 is
Supplied to The processing up to the correction code generation circuit 29 is as follows.
It is similar to the previously proposed application.

The threshold values T1 to T4 from the ROM 25 and the dynamic range DR are supplied to the comparison circuit 31, and the number n of bits allocated to the block is detected by the comparison circuit 31. The allocated bit number n is supplied to the decoding circuit 34.
The dynamic range DR is supplied to the function generation circuit 32. The normalization circuit 30 normalizes the correction code using the function f (DR) from the function generation circuit 32. Function f (DR)
Is f (DR) = DR / const (const ≧ 1).

Therefore, the function f (DR) increases in accordance with the dynamic range DR. The normalization circuit 30 performs normalization by dividing the correction code by f (DR)). Therefore, in a block having a large dynamic range DR, the output signal (correction value) of the normalization circuit 30 is set to be small. The output signal of the normalization circuit 30 is supplied to the addition circuit 33, and the encoded code X0 of the pixel of interest is output.
Is added.

The output signal X0 'of the adding circuit 33 is supplied to a decoding circuit 34 and decoded. The dynamic range DR and the allocated bit number n from the delay circuit 24 are supplied to the decoding circuit 34, and a restoration level corresponding to the output signal X 0 ′ of the adding circuit 33 is obtained from the decoding circuit 34.
The output signal of the decoding circuit 34 is supplied to the adding circuit 35, where the minimum value MIN from the delay circuit 23 is supplied to the adding circuit 33.
Is added.

From the adder circuit 35, a restoration level of the pixel of interest having a level subdivided from the conventional decoding level is obtained. The output signal of the addition circuit 35 is supplied to the block decomposition circuit 36, and the order of the blocks is converted into the order of television scanning. A restoration level is extracted from an output terminal 37 of the block decomposition circuit 36.

FIG. 5 is a flow chart for explaining the operation of the above-described embodiment of the present invention or realizing the present invention by software. In the initial setting step 41, (c = 0, i = 0) is set. In the next step 42, it is determined whether or not Xi> X0 holds. If this holds, c = c + 1 (step 4
3), and the control moves to the next step 44. In step 44, it is determined whether Xi <X0 is satisfied. If this holds, c = c-1 (step 4
5), and the control moves to the next step 46.

Step 46 determines whether or not i ≦ 8. If this is the case, the process returns to step 42 via step 47 where i = i + 1. That is, X1
The above processing is repeated for .about.X8. When the processing of these peripheral coded codes is completed, in step 48, averaging processing of c / 8 is performed. And c ×
A correction code is formed by the normalization step 49 for performing the processing of 0.5. The processing up to this step 49 is the same as that of the previously proposed decoding device.

In step 50 of the next normalization process, the values totalized in the repetition process are divided by the function f (DR). In step 51, it is determined whether the normalized value is c> 0.5. When c> 0.5, c = 0.5. If this is not the case, it is determined in step 53 whether c <-0.5. When c <0.5, c = −0.5.

The processing of these steps 51 to 54 is processing for clipping so that the normalized value falls between -0.5 and +0.5. In step 55, the clipped correction value is the encoded code X0 of the pixel of interest.
Is added to After the addition, the ADRC is decoded.

FIG. 6 shows another embodiment of the present invention. For the sake of simplicity, the portion overlapping with the processing of steps 41 to 54 of the above-described embodiment is represented as a single box. Is omitted. In another embodiment, the correction value processed up to the processing of the clip is supplied to step 56, and DR ≦ 2 ⁿ −1.
Is determined. This dynamic range DR
Is for a block containing the pixel of interest. When this relationship is established in step 56, c = 0 is set in step 57. That is, the correction code is set to 0, and no adaptive decoding is performed. In step 56, when DR ≦ 2 ⁿ −1 does not hold, the correction code c is added to the encoded code X0.

In step 56 of this other embodiment, a block having a small dynamic range DR, specifically, a block having a dynamic range DR smaller than the maximum code value represented by the quantization bit number n is determined. That is, in this block, the code value is (input value−minimum value)
And the distortion should not be increased by adaptive decoding. Therefore, at this time, c = 0
To prevent distortion in the flat part.
For other embodiments, only the flowchart is shown,
As in the case of the embodiment, it can be configured by hardware.

The present invention can be applied to a fixed-length ADRC. In addition, the present invention can be applied to an adaptive decoding apparatus that generates a correction value for an encoded code of a target pixel from encoded codes of peripheral pixels, other than the configuration of the above-described embodiment.

[0048]

According to the present invention, in the ADRC, even if the number of transmitted bits is small, the restoration level can be provided in small steps, so that quantization distortion can be reduced and the edge portion can be reduced. In a block having a large dynamic range, the amount of correction is reduced, so that the resolution of the edge portion can be prevented from deteriorating. Further, the image quality of the decoded image can be improved without increasing the distortion of the flat portion. Furthermore, since the present invention is a process only on the decoding side, there is no need to transmit a special code, and the present invention has an advantage of high efficiency.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an ADRC transmission side to which the present invention can be applied.

FIG. 2 is a schematic diagram used for describing blocks.

FIG. 3 is a schematic diagram used for explaining quantization.

FIG. 4 is a block diagram of one embodiment of the present invention.

FIG. 5 is a flowchart of one embodiment of the present invention.

FIG. 6 is a flowchart for explaining another embodiment of the present invention.

FIG. 7 is a flowchart for explaining a previously proposed decoding device.

FIG. 8 is a schematic diagram used for describing peripheral pixels.

[Explanation of symbols]

 Reference Signs List 21 input terminal 26 peripheral data extraction circuit 27 comparison circuit 28 totalization circuit 29 correction code generation circuit 30 normalization circuit 32 function generation circuit 34 decoding circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/41-1/419 H04N 7/24

Claims (2)

(57) [Claims] 1. Input data is divided into blocks each including a plurality of pixels, and information of each pixel is smaller than an original quantization bit number in accordance with dynamic range information obtained from a maximum value and a minimum value of each block. Coded data, and coded data, and additional information for each block including at least two of the maximum value, the minimum value, and data related to the dynamic range information are transmitted, and based on the transmission data, A decoding device for decoding the encoded data by decoding information relating to the encoded data of the pixel of interest to be decoded;
Comparing means for comparing magnitudes of information related to encoded data of a plurality of peripheral pixels; correction value generating means for generating a correction value based on an output of the comparing means; correction value of an output of the correction value generating means And a means for generating decoded data based on the encoded data of the noted pixel, additional information and the output of the normalizing means. Decoding device. 2. The input data is divided into blocks each including a plurality of pixels, and information of each pixel is smaller than an original quantization bit number in accordance with dynamic range information obtained from a maximum value and a minimum value of each block. Coded data, and coded data, and additional information for each block including at least two of the maximum value, the minimum value, and data related to the dynamic range information are transmitted, and based on the transmission data, A decoding device for decoding the encoded data by decoding information relating to the encoded data of the pixel of interest to be decoded;
Comparing means for comparing magnitudes of information related to encoded data of a plurality of peripheral pixels; correction value generating means for generating a correction value based on an output of the comparing means; correction value of an output of the correction value generating means Is normalized by a function of the dynamic range of the block of the pixel of interest, and a normalizing means for controlling not to perform adaptive decoding using the correction value in the block having a small dynamic range; and Means for generating decoded data based on the encoded data, the additional information, and the output of the normalizing means.