JPH10191332A - Block distortion reducing device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform effective block distortion correction even when block distortion in block DCT encoding, etc., is a small amplitude of about a quantization step. SOLUTION: A calculating circuit 21 calculates activity block stage difference of image data from a terminal 20 and sends it to a block distortion deciding circuit 22 and each pixel correction value calculating circuit 23. A pseudo- random signal generating circuit 27 sends a pseudo-random signal to the circuit 23, switches the correction value at random and sends it to a block distortion correcting circuit 24. The circuit 24 corrects image data from the terminal 20 by using the correction value from the circuit 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a block distortion reduction apparatus and method for reducing block distortion in block coding in which input data such as still image data and moving image data is blocked and subjected to DCT coding or the like. It is about.

[0002]

2. Description of the Related Art Conventionally, block coding such as block DCT (discrete cosine transform) coding has been known as a coding method for efficiently compressing and coding still image data and moving image data.

In the compression / expansion of image data or the like by such block coding, block distortion (block noise) may occur, and the higher the compression ratio, the more likely the distortion is generated. This block distortion is transformed by DCT coding or the like in a closed space within the block and does not consider the correlation beyond the block boundary. The deviation of the reproduction data value at the boundary of is perceived as noise.
Block distortion that occurs when image data is block-coded has a kind of regularity, and is more easily perceived than general random noise, and is a major factor in image quality degradation.

[0004] In order to reduce the block distortion, see, for example, “Ida and Dadatake,“ Noise removal filter in MC-DCT coding method ”, Proc. Of the 1990 IEICE Spring Conference, 7-35”. In the literature, in order to preserve the edges that are the original information of the image and remove those noises, use a quantization step size to determine the on / off of the filter, or process multiple times by changing the processing direction A technique for performing the above is disclosed. Also, in the document of “Izawa,“ Characteristics of Adaptive Noise Removal Filter in Image Block Coding ”, Bulletin of the Faculty of Engineering, Shinshu University, No. 74, pp. 89-100, DCT transform is performed by extracting the surrounding blocks and noise A technique for removing a frequency component has been disclosed.

In the former method, although the processing is simple, the high-frequency component of the image is lost. Therefore, correction without loss of the high-frequency component as in the latter method is desired.

In addition, a method of determining whether or not block distortion has occurred at a block boundary and performing correction using pixel data near the block boundary when block distortion has occurred has been studied. I have.

[0007]

By the way, when the step of the block distortion generated at the block boundary is equal to the quantization step after decoding or has a small amplitude of about several steps,
In some cases, block distortion cannot be effectively corrected.

That is, when the above-mentioned block distortion is minute amplitude and the level of the image data around the block boundary is flat and the above-mentioned block distortion is corrected, the resolution of quantization is limited. In some cases, a pseudo edge may be generated adjacent to a block boundary. If the block distortion is not corrected, the block distortion is not removed, and the step at the block boundary remains as it is.

Even if the level difference of the block distortion is about the quantization step, if the periphery of the block boundary is flat, the distortion appears vertically or horizontally along the block boundary, and is visually recognized. Easy to see.

The present invention has been made in view of such circumstances, and the step of block distortion is one of the quantization steps.
It is an object of the present invention to provide a block distortion reduction apparatus and method capable of effectively reducing or removing block distortion even in the case of a small amplitude of about several steps.

[0011]

According to the present invention, it is determined whether or not block distortion is present, a correction value for reducing block distortion is obtained, and when the distortion is corrected by the correction value based on the determination result,
The above-mentioned problem is solved by modulating the correction value according to the pseudo random signal.

The modulation of the correction value by a pseudo-random signal includes, for example, randomly switching the correction value, and controlling the switching occurrence probability of the correction value according to the distance from the block boundary. .

The image data to be handled includes a luminance signal and a chrominance signal, and blocks generated when block decoding processing such as inverse DCT is performed on coded image data that has been subjected to block coding such as DCT (discrete cosine transform). Distortion is reduced by the present invention.

The block distortion can be reduced only for the luminance signal, only for the color signal, or for both the luminance signal and the color signal. In addition, block distortion reduction may be performed by processing the image data only in the horizontal direction, processing only in the vertical direction, or processing in both the horizontal and vertical directions.

By performing such block distortion reduction, image data near the block boundary is corrected with a randomly modulated correction value. In particular, the distortion can be effectively reduced even when the block distortion has a small amplitude on the order of the quantization step after decoding.

Preferably, the pseudo random signal is reset by a vertical synchronizing signal of an image.
In particular, the adverse effect of adding dynamic noise to a still image can be prevented.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a schematic configuration of a block distortion reduction device according to an embodiment of the present invention.

In FIG. 1, an input terminal 20 is supplied with image data decoded after compression coding including block coding. As a specific example of the image data compression coding method using the block coding, there is a so-called MPEG coding standard. This MPEG
Is ISO / IEC JTC1 / SC29 (Internatio
nal Organization for Standardization / International
al ElectrotechnicalCommission, Joint Technical Com
mittee 1 / Sub Committee 29: Moving Picture Experts G, an organization for studying moving image compression and encoding by the International Standards Organization / International Electrotechnical Commission Joint Technical Committee 1 / Specialized Subcommittee 29)
roup), which is ISO11172 as the MPEG1 standard.
However, there is ISO13818 as the MPEG2 standard. In these international standards, ISO 111
72-1 and ISO13818-1 are ISO11172-2 and IS
O13818-2, and audio items ISO11172-3 and ISO13818
-3 are standardized respectively.

Here, ISO1 as an image compression coding standard is used.
In 1172-2 or ISO13818-2, an image signal is compression-encoded on a picture (frame or field) basis using the correlation in the temporal and spatial directions of the image.
The use of the spatial correlation is realized by using block DCT coding.

As described above, after being subjected to compression coding including block DCT coding and serially transmitted or recorded / reproduced, the data which has been subjected to inverse DCT at the decoder side is supplied to the input terminal 20 in FIG. Is done.

In the activity and block level difference calculation circuit 21 shown in FIG. 1, an activity act which is an average value of a difference between adjacent pixels near a block boundary is described later.
And a block difference δb, which is a difference between adjacent pixels at a block boundary portion, are calculated and sent to the block distortion determination circuit 22.

The block distortion determination circuit 22 performs a condition determination, which will be described later, using the activity act and the block level difference δb to determine whether or not block distortion is present. When it is determined that there is no block distortion, the block distortion correction circuit 24 outputs the data input from the terminal 20 via the terminal 25 without processing the data input from the terminal 20 in accordance with the control signal from the block distortion determination circuit 22. If it is determined that the distortion is a block distortion, the block distortion correction circuit 24 performs a correction process and outputs the result via a terminal 25.

Here, the correction value calculation circuit 23 for each pixel first obtains a correction value α, and then obtains a correction value corresponding to a pixel adjacent to the block boundary and a pixel adjacent thereto, as described later.

When calculating the correction values corresponding to these activities act and each pixel, a pseudo random signal generation circuit 27 using an M (maximum long period) sequence generator or the like without limiting the word length after the decimal point. The rounding process is performed using the pseudo-random signal from the block, and the probability of correcting the block step is controlled according to the distance from the block boundary. This is equivalent to modulating the correction value according to a pseudo random signal or switching the correction value at random.As described later, the occurrence of a pseudo edge at a block boundary is suppressed, and the block step is visually smoothed. In order to be connected to

From a terminal 28, a control signal is sent from a control circuit such as a so-called microcomputer, and the block distortion correction circuit 24
, Control of block distortion removal on / off is performed.
In the pseudo-random signal generation circuit 27, on / off of reset is controlled by VD (vertical synchronization signal) from the terminal 26. For example, when a still image is input, reset by VD is turned on. By resetting the pseudo-random signal generation circuit 27 with this VD, the M-sequence generation pattern between screens becomes the same. That is, when attention is paid to a certain pixel, the correction value for that pixel does not change with time, so that a problem that dynamic noise is added to the corrected image can be prevented.

FIG. 2 shows an example of the internal configuration of the correction value calculation circuit 23 for each pixel in FIG. The activity of FIG. 1, the activity act from the block level difference calculation circuit 21 and the block level difference δb are input to the terminal 30.
The correction value α is calculated by the correction value α calculation circuit 32,
The circuit 33 performs weighting for each pixel, and the adder 34 adds the weight to the pseudo-random signal from the terminal 31.
It is taken out from the terminal 35, and the block distortion correction circuit 2 shown in FIG.
4 The detailed operation of this configuration will be described later.

Here, in order to simplify the explanation, the operation principle of the block distortion reduction in the case of the configuration of FIG. 3 in which the random switching of the correction value by the pseudo random signal in the configuration of FIG. This will be described with reference to FIG.

First, in the activity and block level difference calculating circuit 21 shown in FIG. 3, the activity act and the average value of the difference between adjacent pixels near the block boundary are calculated from the pixel data p of the video signal supplied to the terminal 20. , A block difference Δb, which is the difference between adjacent pixels at the block boundary. Here, as shown in FIG. 4, a pixel near the DCT block boundary, that is, a pixel adjacent to the block boundary and its neighboring pixels are represented by p [i + 4] p [i + 5] p [i + 6] p [i + 7] | p [i + 8] p [i + 9] p
[i + 10] p [i + 11] where | represents a block boundary.

Let the activity act be: act = (| p [i + 6] -p [i + 5] | + | p [i + 7] -p [i + 6] | + | p [i +9] -p [i + 8] | + | p [i + 10] -p [i + 9] |) / 4 (1), and the block step difference δb is given by δb = p [i + 8 ]-p [i + 7]… calculated by (2).

Next, the block distortion determination circuit 22 determines that block distortion is present when the condition of act <δb <Th (3) is satisfied using the activity act and the block level difference δb.
Th in the conditional expression (3) is a predetermined threshold value (threshold value).

When it is determined that there is no block distortion,
In response to the control signal from the block distortion determination circuit 22, the block distortion correction circuit 24 outputs the data input from the terminal 20 without processing.

On the other hand, when it is determined that the distortion is a block distortion, the correction value α of each pixel is first obtained by the following equation (4) or (5).

Α = δb−act: δb> 0 (4) α = δb + act: δb ≦ 0 (5) Next, for each pixel near the block boundary, p ′ [i + 4] = p [i + 4] + α / 16 ... (6) p '[i + 5] = p [i + 5] + α / 8 ... (7) p' [i + 6] = p [i + 6] + α / 4… (8) p '[i + 7] = p [i + 7] + α / 2… (9) p' [i + 8] = p [i + 8] − α / 2… (10 ) p '[i + 9] = p [i + 9]-α / 4 ... (11) p' [i + 10] = p [i + 10]-α / 8 ... (12) p '[i + 11] = p [i + 11] −α / 16 (13) It is obtained by equations (6) to (13).

In the block distortion correction circuit 24, equations (6) to (6) are applied to a pixel adjacent to a block boundary and a pixel adjacent thereto.
Correction is performed according to (13) to remove block distortion.
As a result, the step p ′ [i + 8] −p ′ [i
+7] indicates that the activity act
Is equal to the value of

P ′ [i + 8] −p ′ [i + 7] = (p [i + 8] −α / 2) − (p [i + 7] + α / 2) = (p [i + 8] -p [i + 7])-[alpha] = [delta] b-([delta] b-act) = act (14) FIG. 5 shows an example of the step at the block boundary at this time.
FIG. 5A shows the state before the correction, and FIG.
Shows the state after the correction. The vertical axis in FIG. 5 represents the amplitude, that is, the pixel data value, and the horizontal axis represents H (horizontal).
5A indicates the pixel position in the vertical direction or the V (vertical) direction, and the step δb at the block boundary in FIG. 5A is corrected to the step act at the block boundary in FIG. 5B.

By the way, in the configuration shown in FIG. 3, as shown in FIG. 6, the step of the block distortion is equal to the quantization step after decoding. Consider the correction when is flat.

When such a distortion step is equal to the quantization step, it is determined that the distortion is a block distortion and correction is performed.
Due to the resolution of the quantization, a pseudo edge PE is generated in the vicinity of the block boundary as shown in FIG.

If it is determined that the distortion is not block distortion,
The block distortion is not removed, and the step remains as it is. Although the step of the block distortion is only 1, it is visually noticeable because the periphery of the block boundary is flat and the distortion is arranged vertically or horizontally.

A specific example will be described. When the signal shown in FIG. 6 is input, act = 0 δb = −1, and the threshold value (threshold) Th is set to, for example, 3
If 2 is established, act <δb <32 holds, and it is determined that block distortion occurs. When the correction value α at this time is obtained from the above equation (5), α = −1 + 0 = −1. Therefore, the value of each pixel data in the vicinity of the above-described block boundary is calculated by using the above-described equations (6) to (13).
Equations (15) to (22)
become that way.

[0040]

(Equation 1)

From these equations (15) to (22), a pseudo edge is generated at the pixel of p [i + 7] and p [i + 8] as shown in FIG.

As described above, the correction of the block distortion cannot be performed effectively when the level difference of the block distortion is 1, not limited to the configuration of FIG. .

On the other hand, in the present embodiment,
As shown in FIG. 1, the pseudo random signal generation circuit 27
When calculating the activity act and the correction value corresponding to each pixel by the calculation circuit 23, a pseudo random number using an M (maximum long period) sequence generator or the like is used without limiting the word length after the decimal point. By performing the rounding process using the pseudo random signal from the signal generation circuit 27, the probability of correcting the block step according to the distance from the block boundary is controlled. As a result, the block steps appear visually connected smoothly.

The inside of the correction value calculation circuit 23 of each pixel is configured, for example, as shown in FIG. 2, and the correction value α is calculated by the correction value calculation circuit 32 of FIG. Thereafter, the weighting circuit 33 performs weighting for each pixel.
A specific example of the weighting is a process of bit-shifting the correction value α corresponding to each pixel to obtain values α / 16, α / 8, α / 4, and α / 2.

For example, when the signal shown in FIG. 6 is input, α = −1, so that α / 16, α / 8, α /
4, α / 2 are the values shown in the following (23) to (26), respectively.
The value after the decimal point in binary is also shown.

[0046]

(Equation 2)

From the terminal 31 of FIG. 2, for example, (27)
A pseudo random signal such as a 3-bit M-sequence signal shown in (34) is input. The order of generation of the pseudo-random signals is based on the pseudo-random signal generation circuit 27 of FIG. In the decimal notation, digits are aligned with the correction value of each pixel.

[0048]

(Equation 3)

The adder 34 shown in FIG. 2 adds the correction value of each pixel and a pseudo random signal such as an M sequence. A specific description will be given for each pixel.

The pixels p [i + 7] and p [i + 8] are corrected by α / 2, but carry over when added to the pseudo random signals (31) to (34). Then, the correction value becomes 1. That is, the correction probability is 50%. P [i + 6] of the above pixel
And p [i + 9] are corrected by α / 4, but when they are added to the pseudo random signals (33) and (34), the carry is increased and the correction value becomes 1. That is, the correction probability is 25%. The pixels p [i + 5] and p [i + 10] are corrected by α / 8, but when added to (34) of the pseudo random signal, carry up, and the correction value is 1 Become. That is, the probability of correction is 12.5%. P [i + 4] and p [i + 1]
1] is corrected by α / 16, but does not carry over, so the probability of correction is 0%.

FIG. 8 shows how these corrections are made. In this figure, the point marked with A in the circle is the average level. That is, the value obtained by multiplying each of the correction probabilities by the correction value 1 is a statistically expected correction value, and the result corrected with the expected correction value is shown as the average level. ing. As is clear from FIG. 8, the probability of correction is 5 for the pixels p [i + 7] and p [i + 8] at the block boundary.
At 0%, the statistically expected correction value is 0.5, but the probability of correction decreases as the distance from the block boundary increases, and the pixel p [i + 4] and p [i + 11] There is no correction.

The correction value generated according to the distance from the block boundary as described above is output from the terminal 35.

In this embodiment, the case where the size of the block step is 1 has been described. However, according to the above-described block distortion determination and correction algorithm, the size of the block step is 1 or the quantum level after decoding. Block distortion correction can be performed without particularly discriminating whether or not it is close to the conversion step. Further, it goes without saying that the video signal in the present embodiment can be applied to both a luminance signal and a chrominance signal.

FIG. 9 shows a schematic configuration of a video CD player to which a block distortion reduction circuit according to an embodiment of the present invention can be applied.

In FIG. 9, a video CD or a CD-R
An RF signal read by an optical pickup 102 from a disk 101 such as an OM is input to an RF amplifier 103. The RF signal amplified here is referred to as EFM (8-1
4) The signal is demodulated by a demodulation circuit 104, and enters as a serial data into a disk recording format decoder, for example, a CD-ROM decoder 105.

The CD-ROM decoder 105 converts the serial data into, for example, an MPEG bit stream signal and sends the signal to the MPEG decoder 106. This MPEG
As described above, compression encoding is performed by using the correlation in the time and space directions of an image, and a block DCT code is used to utilize the correlation in the space direction. The MPEG decoder 6 performs decoding in accordance with, for example, the MPEG1 format. At the time of this decoding, the inverse DCT circuit 16
2 performs an inverse DCT process. Further, after performing processing such as interpolation as necessary, the output is performed.

The video signal output from the MPEG decoder 106 is input to a block distortion reduction circuit 107 as a noise reducer. Since the signal here includes noise due to compression / expansion in MPEG1, the block The distortion reduction circuit 107 removes these noises. As the block distortion reduction circuit 107, the embodiment of the present invention as shown in FIG. 1 described above is applied.

After processing by the block distortion reduction circuit 107, N
The TSC encoder 108 performs addition of a synchronization signal, modulation of a color signal, and the like to generate an NTSC video signal. This NT
The SC video signal is output to the output terminal 1 via the D / A converter 109.
It is output to 10.

A control circuit 111 using a microcomputer or the like is provided in connection with the block distortion reduction circuit 107, and a control signal from an operation unit 112 is supplied to the control circuit 111. The operation unit 112 is provided with a control switch for noise reduction, for example, block distortion reduction, and switches on / off of block distortion reduction.

The control circuit 111 controls the reset by the VD (vertical synchronization signal) of the pseudo random signal generation circuit 27 of FIG. 1 such as an M (maximum long cycle) sequence generator. This is because, for example, when a still image is input, by turning on reset by VD and resetting the pseudo random signal generation circuit 27 by VD, it is possible to make the generation pattern of the pseudo random signal between screens the same, Thus, when focusing on a certain pixel, the correction value for that pixel does not change with time, so that a problem that dynamic noise is added to the corrected image can be prevented.

Here, a modification of the above-described embodiment of the present invention will be described.

In this modification, the above equations (6) to (13)
Is changed to the following equations (35) to (40).

P ′ [i + 5] = p [i + 5] + α / 8 (35) p ′ [i + 6] = p [i + 6] + α / 4 (36) p ′ [ i + 7] = p [i + 7] + 3α / 8 ... (37) p '[i + 8] = p [i + 8]-3α / 8 ... (38) p' [i + 9] = p [i + 9] −α / 4 (39) p ′ [i + 10] = p [i + 10] −α / 8 (40) In this modification, the signal shown in FIG. 6 was input. If
α / 8, α / 4, and 3α / 8 take the values shown in (41) to (43), respectively.

[0064]

(Equation 4)

Each pixel p [i + 7] and p [i + 8] shown in FIG.
Is corrected by 3α / 8, but when it is added to the pseudo-random signals of the above equations (32) to (34), the carry increases, and the correction value becomes 1. That is, the correction probability is 37.5%.

In the case of performing the correction according to such a modification, a correction result as shown in FIG.
The block step is corrected more smoothly.

Next, another embodiment of the present invention will be described.
This will be described with reference to FIGS. The present invention can be applied to the correction of the block distortion even if, for example, a configuration as shown in FIGS. 11 and 12 is used. FIG.
Shows a main part of the block distortion reduction circuit 107 in FIG. 9, and FIG. 12 shows a specific example of the block distortion correction circuit 40 in FIG.

The correction method of the embodiment shown in FIGS. 11 and 12 will be described. Block distortion judgment circuit 2
In 2, when it is determined that there is block distortion, the block distortion correction circuit 40 outputs the pixels p [i + 5] and p [i +
6], p [i + 7], p [i + 8], p [i + 9], p [i + 10] for LPF
(Low-pass filter) processing and outputs to the terminal 25. If it is determined that there is no block distortion, the data input from the terminal 20 is output to the terminal 25 without processing.

A specific example of the inside of the block distortion correction circuit 40 will be described with reference to FIG. When the control signal input from the terminal 43 is H (noise reduction on) and the terminal 42
When each of the signals for which the block distortion determination signal is also H (determined as block distortion) is input, the changeover switch 47
Selects a signal on which the following processing has been performed and outputs the signal to a terminal 48. The video signal supplied from the terminal 20 is subjected to, for example, an LPF process having a transfer characteristic represented by the following equation (44).

H (z) = (2 + 3z− ¹ + 6z− ² + 3z− ³ + 2z− ⁴ ) / 16 (44) z− ¹ is a unit delay operator.

When the signal shown in FIG. 6 is input to the LPF, each pixel p [i + 5], p [i + 6], p [i + 7], p [i + 8], p [i +
9] and p [i + 10] have the following values (45) to (50).
Note that p [i + 7] = m + 1 and p [i + 8] = m.

P ′ [i + 5] = (2p [i + 3] + 3p [i + 4] + 6p [i + 5] + 3p [i + 6] + 2p [i + 7]) / 16 = (2 + 3 + 6 + 3 + 2) (m + 1) / 16 = m + 1 ... (45) p '[i + 6] = (2p [i + 4] + 3p [i + 5] + 6p [i + 6] + 3p [ i + 7] + 2p [i + 8]) / 16 = {(2 + 3 + 6 + 3) (m + 1) + 2m} /16=m+0.875 (46) p '[i + 7] = (2p [i + 5 ] + 3p [i + 6] + 6p [i + 7] + 3p [i + 8] + 2p [i + 9]) / 16 = {(2 + 3 + 6) (m + 1) + (3 + 2) m} / 16 = M + 0.6875 ... (47) p '[i + 8] = (2p [i + 6] + 3p [i + 7] + 6p [i + 8] + 3p [i + 9] + 2p [i + 10 ]) / 16 = {(2 + 3) (m + 1) + (6 + 3 + 2) m} /16=m+0.3125 ... (48) p '[i + 9] = (2p [i + 7] + 3p [i + 8] + 6p [i + 9] + 3p [i + 10] + 2p [i + 11]) / 16 = {2 (m + 1) + (3 + 6 + 3 + 2) m} /16=m+0.125… (49) p '[i + 10] = (2p [i + 8] + 3p [i + 9] + 6p [i + 10] + 3p [i + 11] + 2p [i + 12]) / 16 = (2 + 3 + 6 + 3 + 2) m / 16 = m (50) The terminal 41 receives, for example, the 4-bit pseudo random signal shown in (51) to (66). In the decimal display, the digit is aligned with the response value of each pixel.

[0073]

(Equation 5)

In the adder 46, the value subjected to the LPF processing and
Bit pseudo-random signal addition is performed. A specific description will be given for each pixel.

The pixel p [i + 6] in FIG. 4 corresponds to the above (53) to (66)
Carry up when added to the pseudo-random signal of
That is, the probability that the rounded result is m + 1 is 8
7.5%. When the pixel p [i + 7] is added to the pseudo random signal of (56) to (66), the carry is carried out, and the probability of the rounded result being m + 1 is 68.75%. . When the pixel p [i + 8] is added to the pseudo-random signals of (62) to (66), the carry is increased, and the probability of the rounded result being m + 1 is 31.25%. . The pixel p [i + 9] is (6
5) The probability that when the signal is added to the pseudorandom signal of (66) and the result of rounding becomes m + 1 is 12.5
%.

FIG. 13 shows how these corrections are made. The point indicated by A in the circle in the figure is the average level. As described above, the block step is corrected smoothly.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the processing in the horizontal (H) direction has been described, but the same applies to the vertical (V) direction. Applicable to Also, V
The resetting of the pseudo-random signal generator by D (vertical synchronization signal) is not limited to the case where a still image is input, and is applicable to the case where a moving image is input. Further, the correction value α
The correction value is not limited to the above embodiment, and the correction value can be obtained by various methods. For example, a block level difference or block distortion itself may be used as the correction value.

[0078]

According to the present invention, when the distortion is corrected by the block distortion correction value based on the block distortion determination result, the correction value is modulated according to the pseudo random signal. Is corrected with a randomly modulated correction value, the occurrence of a pseudo edge at the block boundary is prevented, and the block steps are visually connected smoothly.

Modulating the correction value with a pseudo random signal includes, for example, switching the correction value at random, and controlling the switching occurrence probability of the correction value according to the distance from the block boundary. . Thus, with simple processing, it is possible to perform correction so that the block step is smoothly connected including the vicinity of the adjacent pixel.

Therefore, according to the present invention, the block DCT
In a device for removing block distortion generated when an image is compressed / expanded using encoding or the like, a simple circuit or method effectively removes block distortion having a small amplitude equivalent to that of a quantization step after decoding. be able to.

Further, by resetting the pseudo-random signal generation by VD (vertical synchronization signal), it is possible to prevent the adverse effect of adding dynamic noise especially in a still image.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an apparatus for reducing block distortion of image data according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a specific configuration example of a correction value calculation circuit for each pixel used in the block distortion reduction device according to the embodiment;

FIG. 3 is a block diagram illustrating a schematic configuration of a block distortion reduction device which is a premise of the embodiment of the present invention.

FIG. 4 is a diagram showing pixels near a block boundary for correcting block distortion.

FIG. 5 is a diagram illustrating an operation of correcting a step at a block boundary.

FIG. 6 is a diagram illustrating an example of pixel data when a step at a block boundary is one quantization step.

FIG. 7 is a diagram illustrating an example of pixel data after correction when a step at a block boundary is one quantization step.

FIG. 8 is a diagram showing an example of pixel data at a block boundary when block distortion reduction is performed according to the embodiment of the present invention.

FIG. 9 is a block diagram showing a schematic configuration of a decoder system using the apparatus for reducing block distortion of image data according to the embodiment of the present invention.

FIG. 10 is a diagram showing an example of pixel data at a block boundary when block distortion reduction is performed according to a modification of the embodiment of the present invention.

FIG. 11 is a block diagram showing a schematic configuration of an image data block distortion reduction apparatus according to another embodiment of the present invention.

12 is a block diagram illustrating a specific configuration example of a block distortion correction circuit used in the block distortion reduction device according to the embodiment of FIG. 11;

13 is a diagram illustrating an example of pixel data at a block boundary when block distortion reduction is performed according to the embodiment of FIG. 11;

[Explanation of symbols]

21 Activity block level difference calculation circuit, 22
Block distortion determination circuit, 23 correction value calculation circuit for each pixel, 24 block distortion correction circuit, 27 pseudo random signal generation circuit

Claims (10)

[Claims] 1. A block distortion reduction apparatus for reducing block distortion in block encoding of image data, comprising: a determination unit for determining whether or not block distortion is present; and a correction for obtaining a correction value for reducing the block distortion. Value correction means, correction means for correcting distortion with the correction value based on the determination result by the determination means, and pseudo-random signal generation means, wherein the correction value calculation means generates the pseudo-random signal from the correction value. A block distortion reducing device comprising means for modulating according to a pseudo random signal from the means. 2. The block distortion reduction device according to claim 1, wherein said correction value calculation means controls a probability of correction by said correction value according to a distance from a block boundary. 3. The apparatus according to claim 1, wherein the input image data comprises a luminance signal and a chrominance signal, and said at least one of said luminance signal and said chrominance signal is corrected for said distortion reduction. Block distortion reduction device. 4. The block distortion reduction device according to claim 1, wherein the correction for reducing the distortion is performed on at least one of the horizontal direction and the vertical direction of the image data. 5. The apparatus according to claim 1, wherein said pseudo-random signal generating means is reset by a vertical synchronizing signal of image data. 6. A block distortion reduction method for reducing block distortion in block coding of image data, comprising: a determination step of determining whether block distortion is present; and a correction value for reducing the block distortion. A correction value calculation step, a correction step of correcting distortion with the correction value based on the determination result in the determination step, and a step of generating a pseudo random signal. A block distortion reduction method characterized by modulating according to a generated pseudo random signal. 7. The block distortion reduction method according to claim 6, wherein said correction value calculating step controls a probability of correction by said correction value according to a distance from a block boundary. 8. The apparatus according to claim 6, wherein the input image data comprises a luminance signal and a chrominance signal, and at least one of said luminance signal and said chrominance signal is corrected for said distortion reduction. Block distortion reduction method. 9. The method according to claim 6, wherein the correction for reducing the distortion is performed on at least one of the horizontal direction and the vertical direction of the image data. 10. The method according to claim 6, wherein said pseudo random signal generating step is reset by a vertical synchronization signal of image data.