JP2001339720A - Image information conversion apparatus and method for same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correspond to a change of complexity in GOP. SOLUTION: The device of the present invention transcodes MPEG 2 image compression information (bit stream) of interlaced scanning to MPEG 4 image compression information (bit stream) of sequential scanning, wherein average quantization scale calculating unit 25 finds an approximate value of average quantization scale relative to each frame using information quantizer-scale-code contained in slice header within MPEG 2 image compression information (bit stream) that has been taken out by slice header analyzing unit 18, a complexity calculating unit 26 finds an approximate value of complexity relative to each frame using these encoding amount (bit number) assigned to each frame, and MPEG 4 image information encoding unit (I/P-VOP) controls encoding amount of MPEG 4 image compression information (bit stream) using approximated complexity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image information conversion apparatus and method for converting image information, and more particularly, to image information (bit stream) such as MPEG compressed by orthogonal transform such as discrete cosine transform and motion compensation. And a method for converting image information used when receiving an image via a network medium such as satellite broadcasting, cable TV, or the Internet, or when processing the same on a storage medium such as an optical disk or a magnetic disk. .

[0002]

2. Description of the Related Art In recent years, image information is handled as digital data, and for the purpose of transmitting and storing information with high efficiency, compression is performed by orthogonal transform such as discrete cosine transform and motion compensation using redundancy inherent in image information. An image information compression system such as MPEG is provided. Then, an apparatus conforming to such an image information compression method is used for information distribution of a broadcasting station or the like,
It is becoming widespread in both information reception in general households.

In particular, MPEG2 (ISO / IEC 13
818-2) is defined as a general-purpose image encoding method that covers both interlaced scan images and progressive scan images, as well as standard resolution images and high definition images.

That is, according to the MPEG2 encoding and compression system, for example, a code amount (bit rate) of 4 to 8 Mbps is assigned to a standard resolution interlaced scan image having 720 × 480 pixels, and a high resolution having 1920 × 1088 pixels is assigned. By assigning a code amount (bit rate) of 18 to 22 Mbps to the interlaced scan image, a high compression rate and good image quality can be realized.

[0005] For these reasons, it is expected that MPEG2 will be used in a wide range of applications for professional use and consumer use. However, MPEG2 is mainly intended for high-quality coding suitable for broadcasting, and does not support, for example, a coding amount (bit rate) lower than that of MPEG1, that is, a coding method with a higher compression rate.

[0006] On the other hand, with the spread of portable terminals in recent years, it is expected that the need for an encoding system with a high compression ratio will increase in the future, and in response to this, standardization of the MPEG4 encoding system with a high compression ratio has been carried out. Have been done. Regarding this image coding method, ISO / IEC 14
International standard was approved as 496-2.

By the way, MPEG2 image compression information (bit stream) once encoded for digital broadcasting
There is a need to convert image compression information (bit stream) having a lower code amount (bit rate), which is more suitable for processing on a mobile terminal or the like.

In order to achieve such an object, “Field-to
-Frame Transcoding with Spatialand Temporal Downsa
mpling ”(Susie L Wee, John G. Apostolopoulos, and N
ickFeamster, ICIP 99, hereafter referred to as Document 1).
And an image information conversion device (transcoder) is provided.
I have.

[0009] As shown in FIG. 5, an image information conversion device (transcoder) provided in Document 1 includes a picture type discrimination unit 1, an MPEG2 image information decoding unit (I / P picture) 2, a thinning-out unit. It comprises a unit 3, an MPEG4 image information encoding unit (I / P-VOP) 4, a motion vector synthesizing unit 5, and a motion vector detecting unit 6.

[0010] The image information conversion apparatus includes an intra-coded image (I picture; I) encoded in a frame,
A forward predictive coded image (P picture; P) predictively coded by referring to the forward direction in the display order, and a bidirectional predictive coded image predictively coded by referring to the forward and reverse directions in the display order MPEG-2 image compression information (bit stream) of interlaced scanning composed of (B picture; B) is input.

[0011] The MPEG2 image compression information (bit stream) is supplied to an I / P
It is determined whether the picture is related to a picture or a B picture.
Output to the image information decoding unit (I / P picture) 2
The picture is discarded.

The processing in the MPEG2 image information decoding section (I / P picture) 2 is to decode the MPEG2 image compression information (bit stream) into an image signal, as in a normal MPEG2 image information decoding device.

A pixel value output from the MPEG2 image information decoding unit (I / P picture) 2 is input to a thinning unit 3. The thinning section 3 performs a 1/2 thinning process in the horizontal direction, and leaves only one of the data of the first field and the second field in the vertical direction, and discards the other. By such thinning, a progressively scanned image having a size of ４ of the input image information is generated.

The progressively scanned image generated by the thinning section 3 is converted to an MPEG4 image information encoding section (I / P-VOP) 4
Is encoded into an I-VOP encoded in the frame and a P-VOP predicted and encoded with reference to the forward direction in the display order, and output as MPEG4 image compression information (bit stream). VOP is Video object Pla
ne, which corresponds to a frame in MPEG2.

At this time, the motion vector information in the input MPEG2 image compression information (bit stream) is mapped to a motion vector for the decimated image information in the motion vector synthesizing unit 5 and the motion vector detecting unit 6
In, a highly accurate motion vector is detected based on the motion vector value synthesized by the motion vector synthesizing unit 5.

Reference 1 discloses an image information conversion apparatus for generating MPEG4 image compression information (bit stream) of a progressively scanned image having a size of 1/2 × 1/2 of the input MPEG 2 image compression information (bit stream). Is described. That is, for example, the input MPEG2 image compression information (bit stream) is transmitted using NTSC (National Telev.
If it complies with the standards of the ISion Committee, the output MPEG4 image compression information has an SIF size (352 × 240 pixels).

In the image information conversion apparatus shown in FIG. 5, an MPEG4 image information encoding unit (I / P-V
OP) 4 is to control the amount of code to output MPEG4
This is a major factor in determining the image quality of the image compression information (bit stream). ISO / IEC 14496-
In No. 2, the code amount control method is not specified, and each vendor has
It is possible to use a method that is considered optimal in terms of the amount of calculation and the output image quality. In the following, MPEG2 Test Model 5 (IS
O / IEC JTC1 / SC29 / WG11 N040
The method described in 0) will be described.

The flow of this code amount control will be described with reference to the flow shown in FIG. In the first step S11,
The image information encoding unit (I / P-VOP) 4 includes a target code amount (target bit rate) and a GOP (groove).
f pictures) configuration, and allocates bits to each picture. Here, a GOP is a set of pictures that can be randomly accessed.

That is, in step S11, the image information encoding unit (I / P-VOP) 4 determines the amount of bits allocated to each picture in the GOP, including the picture to be allocated, of the picture not yet decoded in the GOP. Are allocated based on the amount of bits allocated to (hereinafter referred to as R). This distribution is repeated in the order of the coded pictures in the GOP. At this time, the code amount is assigned to each picture using the following two assumptions.

First, it is assumed that the product of the average quantization scale code used when encoding each picture and the generated code amount becomes a constant value for each picture type unless the picture changes. Therefore, after encoding each picture, a variable X indicating the complexity of the screen is set for each picture type.
_i, X _p, updated by X _b (grobal complelxity measure) the following equation (1).

[0021]

(Equation 6)

Where S_i, S_p, S_bIs for picture encoding
Is the amount of generated code bits, and Q_i, Q _p, Q_bIs a picture
This is an average quantization scale code at the time of key coding. Also,
The initial value is the target code amount (target bit rate) bi
Using t_rate [bits / sec], equation (2)
The value is indicated by

[0023]

(Equation 7)

Second, when the ratios K _p and K _b of the quantized scale codes of the P and B pictures with respect to the quantized scale code of the I picture are equal to the values defined in the equation (3), the whole is always obtained. Assume that the image quality is optimized.

[0025]

(Equation 8)

That is, the quantization scale code of the B picture is always 1.4 times the quantization scale code of the I and P pictures. This is because the picture quality of the I and P pictures is improved by adding the code amount that can be saved in the B picture to the I and P pictures by coding the B picture somewhat coarsely compared to the I and P pictures. It is assumed that the image quality of the B picture that refers to this is also improved.

Based on the above two assumptions, the bit amount (T _i , T _p , T _b ) allocated to each picture of the GOP is a value shown in equation (4).

[0028]

(Equation 9)

Here, N _p and N _b are the numbers of P and B pictures which have not been encoded in the GOP.

Each time each picture is coded according to steps S11 and S12 based on the allocated code amount obtained in this manner, the bit amount R allocated to the uncoded picture in the GOP is calculated by the equation (5). ) To update.

[0031]

(Equation 10)

When encoding the first picture of the GOP, R is updated by equation (6).

[0033]

[Equation 11]

N is the number of pictures in the GOP. Also,
The initial value of R at the beginning of the sequence is 0.

Next, in step S12, the image information encoding device (I / P-VOP) 4 performs rate control using the virtual buffer. That is, in step S12, the image information encoding device (I / P-VOP) 4 allocates bits (T _i , T _p , T _b ) for each picture obtained by equation (4) in step S11, In order to match the actual generated code amounts, the quantization scale code is obtained by macroblock-based feedback control based on the capacity of three types of virtual buffers independently set for each picture.

First, prior to encoding the j-th macroblock, the occupancy of the virtual buffer is determined by equation (7).

[0037]

(Equation 12)

Here, d ₀ ⁱ , d ₀ ^p , and d ₀ ^b are the initial occupancy of each virtual buffer, B _j is the amount of generated bits from the head of the picture to the j-th macroblock, and MB_cnt is the number of bits in one picture. This is the number of macro blocks. Virtual buffer occupancy at the end of each picture encoding (d _{MB_cnt} ⁱ , d _{MB_cnt} ^p ,
d _{MB_cnt} ^b ) is used as an initial value (d ₀ ⁱ , d ₀ ^p , d ₀ ^b ) of the virtual buffer occupancy for the next picture of the same picture type.

Next, the quantization scale code for the j-th macroblock is calculated by equation (8).

[0040]

(Equation 13)

Here, r is a variable called a reaction parameter that controls the response of the feedback loop, and is given by equation (9).

[0042]

[Equation 14]

The initial value of the virtual buffer at the start of encoding is given by equation (10).

[0044]

(Equation 15)

Finally, in step S13, the image information encoding device (I / P-VOP) 4 performs adaptive quantization for each macroblock in consideration of visual characteristics. That is,
In step S13, the image information encoding unit (I / P-
VOP) 4 is to quantize the quantized scale code obtained in step S12 more finely in a flat portion where the deterioration is conspicuous visually and coarsely in a complicated portion of the picture where the deterioration is relatively inconspicuous. , And is changed by a variable called an activity for each macroblock.

The activity is calculated by using the pixel value of the luminance signal of the original picture and the pixel values of a total of 8 blocks of 4 blocks in the frame discrete cosine transform mode and 4 blocks in the field discrete cosine transform mode. Given by (11).

[0047]

(Equation 16)

Here, P _k is the pixel value in the luminance signal block of the original image. The minimum value in the equation (11) is
This is because the quantization is made fine when there is a flat portion even in only a part of the macro block.

Further, according to equation (12), the value is 0.5 to
A normalization activity Nact _j having a range of 2 is obtained.

[0050]

[Equation 17]

Here, avg_act is the average value of act _j in the picture coded immediately before.

The quantized scale code mquant _j taking into account the visual characteristics is given by equation (13) based on the quantized scale code Q _j obtained in step S12.

[0053]

(Equation 18)

It is known that the above-mentioned code amount control method defined in the MPEG2 Test Model 5 has the following restrictions, and when performing actual control, it is necessary to take measures against these restrictions. That is, the first limitation is that the first step S11 cannot respond to a scene change, and the third step S1
This means that the parameter avg_act used in step 3 has an incorrect value. The second limitation is that MPEG2 and MP
VBV (VideoBuffer Ve) specified in EG4
rifier) is not guaranteed.

By the way, the document "Theoretical analysis of MPEG compression efficiency and its application to code amount control" (IEICE Technical Report, IE-9).
5, DSP95-10, May 1995, hereinafter referred to as Reference 2).
The code amount control method defined in model 5 is MP
The EG-2 image encoding device does not always provide good image quality.

This document 2 proposes the following method as a method for giving an optimal code amount distribution for each frame in a GOP, particularly for giving a good image quality.
That is, let N _I , N _P , and N _B be the numbers of I, P, and B pictures that have not been encoded in the GOP, and let R _I , R _P , and R _B be the code amounts assigned to these.
Also, under the fixed rate condition given by equation (14),
Q _I , Q _P , Q
_B, and m is an order relating the quantization step size and the reproduction error variance (that is, the quantization step size is m
It is assumed that minimizing the average value of the powers will minimize the reproduction error variance). Then, consider minimizing equation (15).

[0057]

[Equation 19]

[0058]

(Equation 20)

The average quantization scale Q and the code amount R in each frame are represented by Test Model.
5 is related to the complexity X of each frame, which is also a medium variable used in Expression 5, as shown in Expression (16).

[0060]

(Equation 21)

The formula (1) is also taken into consideration while considering the relationship of the formula (16).
R _I , which minimizes equation (15) under the constraint of 4)
When R _P and R _B are calculated using the Lagrange's undetermined multiplier method, the following values are obtained as optimal R _I , R _P and R _B.

[0062]

(Equation 22)

When α = 1, equation (17) and MPEG2
It can be said that the relationship with Expression (4) in the code amount control method defined in Test Model 5 is as follows. That is, equation (17) uses the parameters K _p and K _b that are the code amount control parameters as the complexity X _I ,
X _P, according to X _B, nothing but that they are adaptively calculated as in Equation (18).

[0064]

(Equation 23)

In Reference 2, as the value of 1 / (1 + m),
It is shown that good image quality can be obtained by setting the value to about 0.6 to 1.2.

[0066]

However, in the image information conversion device shown in FIG. 5, the MPEG2 T information is encoded by the MPEG4 image information encoding device (I / P-VOP) 4.
When code amount control is performed using a method similar to that defined in est Model 5, it is impossible to cope with a change in complexity within the GOP due to a scene change or the like. For this reason, stable code amount control becomes difficult, which may cause image quality degradation. In addition, this image information conversion device has a problem that the amount of calculation processing is large.

The present invention has been proposed in view of the above-mentioned circumstances, and is capable of coping with a change in complexity within a GOP, and an image information conversion apparatus and a method for reducing the amount of arithmetic processing. The aim is to provide a method.

[0068]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an interlaced scan input image compression information compressed by a first compression encoding system by a second compression encoding system. The input image compression information is converted into compressed progressively scanned output image compression information. The input image compression information is compressed by using the quantization scale information included in a predetermined position of the input image compression information compressed by the first compression encoding method. The approximate value of the average quantization scale of each frame of the image compression information is obtained, and the approximate value of the complexity of the image of the frame is obtained by using the approximate value and the code amount assigned to each frame. The code amount in the coding of the output image compression information is controlled on the basis of this.

According to the present invention, MPEG2 image compression information (bit stream) of interlaced scanning is used as input image compression information, and MPEG4 image compression information (bit stream) of sequential operation is used as output image compression information. The MPEG2 image compression information (bit stream) and the MPEG4 image compression information are composed of a pixel block sequence, that is, a slice. This slice is composed of a pixel block composed of a plurality of pixels, that is, a macroblock.

The present invention provides a picture type discriminating section for discriminating the type of an image of MPEG2 image compression information.
A compression information analysis unit for analyzing compression information of image compression information, a slice header analysis unit for analyzing a slice header which is a component thereof, an image compression information decoding unit (I / P picture) for decoding MPEG2 image compression information, and a pixel. Thinning unit for thinning, MPEG encoding to MPEG4 image compression information
4 image information coding unit (I / P-VOP), a motion vector synthesizing unit for synthesizing the motion vector of the MPEG2 image compression information, a motion vector detecting unit for detecting the motion vector, and the compression information sent from the compression information analyzing unit. It also has an information buffer for storing, an average quantization scale calculation unit for calculating an average quantization scale, and a complexity calculation unit for calculating complexity based on the average quantization scale.

The present invention uses the quantizer_scale_code present in each slice header to approximately calculate the average quantization scale of the entire screen, and calculates the input MPEG2 image compression information (bit MPEG4 image compression information (bits) of progressive scanning in a state where the code amount allocation for each frame is optimized for the image with a smaller amount of processing using the approximate value of the complexity for each frame in the stream). Stream).

In the picture type discriminating section having the above-described structure, only the I / P picture is left in the input MPEG2 image compression information (bit stream).
Pictures related to pictures are discarded, and the compression information analyzer realizes a delay of one GOP, and outputs M
In the PEG2 image compression information (bit stream), the code amount (bit number) allocated to each frame is detected, and in the slice header analysis unit in the compression information analysis unit, quantizer_scale_ in the slice header is determined.
The value of code is extracted, and the MPEG2 image information decoding unit (I /
(P picture), the compression information (bit stream) relating to the I / P picture, which is output from the picture type discriminating unit, is obtained by using all the 8th-order discrete cosine coefficients in the horizontal and vertical directions, or a low-frequency component thereof. The decoding process using only MPEG-2 is performed.
To extract only the first field or the second field of the image information output from the two-image information decoding unit (I / P picture) and convert it to a sequentially scanned image, and at the same time to convert it to a desired image frame size Is downsampled, and the MPEG4 image information encoding unit (I / P-VOP) converts the image information to be output from the thinning device to MPEG.
In the motion vector synthesizing unit, based on the motion vector value in the input image compression information (bit stream) detected by the MPEG2 image information decoding unit (I / P picture). Perform mapping to the motion vector value for the image data after scan conversion,
The motion vector detecting section performs high-precision motion vector detection based on the motion vector value output from the motion vector synthesizing section. In the information buffer, the input MPEG2 image extracted by the compression information analyzing section. In the compression information (bit stream), the code amount (the number of bits) allocated to each frame is stored. In the average quantization scale calculation unit, the quantizer_scale_co for each slice extracted in the slice header analysis unit is stored.
From the de, the average quantization scale for each frame is approximately calculated, and the complexity calculating unit allocates the average quantization scale to each frame in the input image compression information (bit stream) stored in the information buffer. The complexity for each frame is approximately calculated from the code amount (the number of bits) and the average quantization scale for each frame approximately calculated by the complexity calculation unit, and the MPEG4 image information encoding unit ( I /
(P-VOP) as a parameter for code amount control.

[0073]

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

First, an example of an image information conversion device (transcoder) will be described with reference to FIG.

The image information conversion apparatus includes a picture type discriminating unit 7, a compression information analyzing unit 8, an MPEG2 image information decoding unit (I / P picture) 9, a thinning unit 10,
A PEG4 image information encoding unit (I / P-VOP) 11;
Motion vector synthesis unit 12 and motion vector detection unit 13
, Information buffer 14 and complexity calculating unit 15
It is composed of

The image information conversion apparatus includes an intra-coded image (I picture; I) encoded in a frame,
A forward predictive coded image (P picture; P) predictively coded by referring to the forward direction in the display order, and a bidirectional predictive coded image predictively coded by referring to the forward and reverse directions in the display order MPEG-2 image compression information (bit stream) of interlaced scanning composed of (B picture; B) is input.

The MPEG2 image compression information (bit stream) is transmitted to the I / P
It is determined whether it is related to a picture or a B picture, and only the I / P picture is output to the subsequent compression information analyzer 8, and the B picture is discarded.

In the compression information analysis unit 8, the average value Q over the entire frame of the quantization scale used for the decoding processing in the MPEG2 image information decoding device (I / P picture) 8, and the MPEG2 image compression information to be input In the (bit stream), the total code amount (the number of bits) B allocated to the frame is stored in the information buffer 14.

The processing in the MPEG2 image information decoding section (I / P picture) 9 decodes the MPEG2 image compression information (bit stream) into an image signal, similarly to a normal MPEG2 image information decoding device. Where B
Since data relating to pictures is discarded in the picture type discriminating unit 7, the MPEG2 image information decoding unit (I / P picture) 1 only needs to have a function capable of decoding only I / P pictures.

The pixel value output from the MPEG2 image information decoding unit (I / P picture) 9 is input to the thinning unit 10. The thinning section 10 performs a 1/2 thinning process in the horizontal direction, and leaves only one of the data of the first field and the second field in the vertical direction, and discards the other. By such thinning, a progressively scanned image having a size of ４ of the input image information is generated.

By the way, the image output from the thinning section 10 is converted into an MPEG4 image information encoding section (I / P-VOP) 1
In order to perform encoding in units of macroblocks composed of 16 × 16 pixels in 1, the number of pixels must be a multiple of 16 in both the horizontal and vertical directions. In the thinning section 10, the pixels are supplemented or discarded for this purpose simultaneously with the thinning.

For example, if the input MPEG2 image compression information (bit stream) is NTSC (National Televis)
In the case of an image conforming to the standards of the Ion System Committee, that is, an interlaced scan image of 720 × 480 pixels and 30 Hz, the image frame after thinning out has an SIF (360 × 240 pixels) size. For this image, the thinning unit 3 discards, for example, the eight lines at the right end or the left end in the horizontal direction to obtain 352 × 240 pixels.

By changing the operation of the thinning section 10, other image frames, for example, about 1 in the above example, can be used.
It is also possible to convert the image into an image of QSIF (176 × 112 pixels) which is an image frame of ××.

Further, the above-mentioned reference 1 discloses that the processing in the MPEG2 image information decoding unit (I / P picture) 9 includes, in each of the horizontal and vertical directions, the MPEG2 image compression information (bit stream) in the input. 8
An image information conversion apparatus that performs decoding processing using all of the following discrete cosine transform coefficients is described. However, the description is not limited to the apparatus illustrated in FIG. 1. Only the horizontal direction, or both the horizontal and vertical directions, By performing decoding using only low-frequency components of the eighth-order discrete cosine transform coefficients, it is possible to reduce the amount of computation and video memory capacity involved in decoding while minimizing image quality degradation.

The progressive scan image generated by the thinning unit 10 is an MPEG4 image information encoding unit (I / P-VOP)
11 and an I-VOP coded in the frame and a P-VO coded predictively with reference to the forward direction in the display order.
P is encoded and output as MPEG4 image compression information (bit stream).

VOP means Video Object Plane, which corresponds to a frame in MPEG2. Further, I-VOP is an intra-coded VOP corresponding to an I picture, P-VOP is a forward predictive coded VOP corresponding to a P picture, and B-VOP is a bidirectional predicted coded VOP corresponding to a B picture.

The MPEG4 image information encoding unit (I / P-V
OP) 11, the input MPE
The motion vector information in the G2 image compression information (bit stream) is mapped to a motion vector for the decimated image information in the motion vector synthesizing unit 12, and the motion vector synthesizing unit 1 in the motion vector detecting unit 13.
2, a highly accurate motion vector is detected based on the motion vector value synthesized.

The MPEG4 image information encoding unit (I /
The P-VOP) 11 receives an approximate value of the complexity from the complexity calculating unit 15, and calculates a target code amount (target bit) for each VOP based on the approximate value. Encoding is performed according to the target bit).

In the complexity calculating section 15,
From the information Q and B for each frame stored in the information buffer 14, the complexity X for the frame is calculated by equation (19).

[0090]

(Equation 24)

The complexity X for the frame calculated by the equation (19) is 1 GOV (group
After being buffered for the amount of VOPs), it is transmitted to the MPEG4 image information encoding unit (I / P-VOP) 11 as a parameter for controlling the code amount. Therefore, a delay of 1 GOV is required. This delay is realized using a delay buffer (not shown). Here, GOV is a set of VOPs that can be randomly accessed.

In the following, the complexity X for each frame in the GOV calculated in equation (19) will be described.
Is an MPEG4 image information encoding unit (I / P-VOP) 1
1 will be described.
In the following, a case where the picture type determination unit 7 does not exist in the image information conversion apparatus and does not perform the frame rate conversion will be considered.

The meaning of K _P and K _B obtained by the equation (18) means that P-VOP / B-VO for the ideal average quantization scale Q _{i_ideal} for I-VOP.
Ideal average quantization scale Q _{p_ideal} , Q for P
_That is, the ratio of _{b_ideal} is given by equation (20).

[0094]

(Equation 25)

The MPEG2 Test Model 5 does not adaptively calculate K _p and K _b as in equation (18), but uses a fixed value as shown in equation (3).

From equations (18) and (20), a certain VO
Let P 1 and the complexity for a certain VOP 2 be X ₁ and X ₂ respectively, and let the ideal quantization scale be Q
_Assuming that _{1_ideal} and Q _{2_ideal} , equation (21) is obtained.

[0097]

(Equation 26)

Alternatively, MPEG2 Test Mod
When it is desired to use the fixed value shown in the equation (3) as in el 5, the equation (22) may be used instead of the equation (21).

[0099]

[Equation 27]

Now, let R be the total code amount (the number of bits) allocated to the uncoded VOP in the GOV.
Are assigned to each VOP as R ₁ , R ₂ ,... R _n , the image quality for the GOV is optimized. Here, a relational expression such as Expression (23) is established between R and R ₁ , R ₂ ,... R _n .

[0101]

[Equation 28]

[0102] Some VOP average quantization scale for _k Q _k, assigned code amount R _k, between the complexity X _k Note also that there is a relation of equation (24), formula (23)
Equation (25) is obtained by transforming

[0103]

(Equation 29)

[0104]

[Equation 30]

In equation (25), regarding K (X ₁ , X ₂ ), even if the value shown in equation (21) is used, equation (22)
May be used, but the former can realize more optimal code amount distribution according to the image. At this time, by setting the value of 1 / (1 + m) to 1.0, it is not necessary to perform an exponential operation, and high-speed execution is possible. Even when the value of 1 / (1 + m) is set to a value other than 1.0, high-speed execution can be performed by holding a table in advance and performing an exponential operation with reference to the table.

The complexity X _k for each VOP in the equation (25) is based on the MPEG4 image coding. The complexity for each frame based on the MPEG2 image coding and the complexity for each frame based on the MPEG4 image coding are shown. Assuming that the cities are equal, it is possible to calculate the target code amount for the VOP by using equation (25) by using X _k stored in the complexity calculating unit 15.

FIG. 2 shows a flow of calculating the target code amount. In the first step S21, the compression information analysis unit 8
Extracts an average quantization scale Q and an allocated code amount (number of bits) B for each frame in a GOP used for decoding processing in the MPEG2 image information decoding unit 9.

In step S22, the complexity calculating section 15 calculates a complexity X given by the product of the average quantization scale Q and the allocated code amount (number of bits) B.

In step S23, the MPEG4 image encoding unit (I / P-VOP) 11 calculates a target code amount (target bit) according to the complexity X.

In MPEG2 Test Model 5, it is assumed that the complexities X _i , X _p , and X _b for the I, P, and B pictures in the GOP are constant, but a scene change is actually included in the GOP. Or
This assumption does not hold when the background changes significantly in the GOP, hinders stable code amount control, and causes image quality deterioration. In the image information conversion apparatus shown in FIG. 1, even in such a case, the code amount control based on the complexity for each frame in the input MPEG2 image compression information (bit stream) is performed. , It is possible to perform stable code amount control.

Next, another example of the image information conversion apparatus will be described with reference to FIG.

This image information conversion apparatus includes a picture type discrimination section 16, a compression information analysis section 17 having a slice header analysis section 18, and an MPEG2 image information decoding section (I /
P picture) 19, a thinning-out unit 20, an MPEG4 image information encoding unit (I / P-VOP) 21, a motion vector combining unit 22, a motion vector detecting unit 23, an information buffer 24, an average quantization scale It comprises a calculation unit 25 and a complexity calculation unit 26.

In FIG. 3, the operations other than the code amount control in the compression information analysis unit 17, slice header analysis unit 18, information buffer 24, average quantization scale calculation unit 25, and complexity calculation unit 26 are shown in FIG. Since the configuration is the same as that of the image information conversion apparatus shown, the operation of controlling the code amount by these will be mainly described below.

In the compression information analysis unit 17, for the MPEG2 image compression information (bit stream) consisting of only the I / P pictures input from the picture type discrimination unit 16, the code amount (bit stream) allocated to each frame Information B on the number of bits is extracted, and this information is transmitted to the information buffer 24. At the same time, the compression information analyzer 1
7, the slice header analysis unit 18 receives the input MPEG2 image compression information (bit stream).
In the, the slice layer is parsed, and the quantizer_scale_code
Is extracted and transmitted to the average quantization scale calculation unit 25.

Here, a slice is a macroblock sequence constituting an image of MPEG2 image compression information (bit stream), and quantizer_scale_code indicates a quantization scale of the first macroblock included in the slice.

The processing in the MPEG2 image information decoding section (I / P picture) 19 is for decoding the MPEG2 image compression information (bit stream) into an image signal, similarly to a normal MPEG2 image information decoding apparatus.

The pixel value output from the MPEG2 image information decoding section (I / P picture) 19 is input to the thinning section 20. The thinning unit 20 performs 1/2 thinning processing in the horizontal direction, leaves only data of one of the first field and the second field in the vertical direction, and discards the other. By such thinning, a progressively scanned image having a size of ４ of the input image information is generated.

The progressive scan image generated by the thinning section 20 is an MPEG4 image information encoding section (I / P-VOP)
21 and an I-VOP encoded in a frame and a P-VO encoded by prediction with reference to the forward direction in the display order.
P is encoded and output as MPEG4 image compression information (bit stream).

The MPEG4 image information encoding unit (I / P-V
OP) 21, the input MPE
The motion vector information in the G2 image compression information (bit stream) is mapped to a motion vector for the decimated image information in the motion vector synthesizing unit 22, and in the motion vector detecting unit 23,
2, a highly accurate motion vector is detected based on the motion vector value synthesized.

Further, the MPEG4 image information encoding section (I /
The P-VOP) 21 receives an approximate value of the complexity from the complexity calculating unit 26, and calculates a target code amount (target bit) for each VOP based on the approximate value, and calculates the target code amount (target bit amount). Encoding is performed according to the target bit).

In the average quantization scale calculation unit 25, q which is the quantizer_scale_code for each slice
_Slice _j, and than the number N _{sli ce} of slices included in each frame, the approximate value Q _ESTI average quantizer scale for each frame is calculated by the equation (26).

[0122]

(Equation 31)

In the complexity calculating section 26,
Information B on the code amount (the number of bits) allocated to each frame stored in the information buffer 24;
And, in the average quantization scale calculation unit 25, the expression (2)
Using Q _esti for each frame calculated in 6), an approximate value X _esti of the _complexity for each frame is calculated by equation (27).

[0124]

(Equation 32)

The complexity calculating section 26 calculates the complexity X _{k_esti} for each VOP in one GOV calculated by the equation (27), and transmits the complexity X _{k_esti} to the MPEG4 image information coding section (I / P-VOP) 21. , Equation (2)
As X _k in 5), used to calculate the target code amount (target bit) for each VOP. FIG.
, An MPEG4 image information encoding unit (I / P-VOP) 1
4 shows a series of flows for calculating a target code amount (target bits) for each VOP in FIG.

In the first step S31, the compression information analyzer 17 analyzes the syntax of MPEG2 image compression information (bit stream). In step S32, the information buffer 24 stores the code amount (the number of bits) B assigned to each frame, which is clarified by the syntax analysis in step S31.

On the other hand, in step S33, the slice header analysis unit 18 provided in the compression information analysis unit 17
The quantizer_scale_code in the slice header of the MPEG2 image compression information (bit stream) is extracted. In step S34, the average quantization scale calculation unit 25
Is the quantize extracted by the slice header analysis unit 18.
Based on R_scale_code, to calculate the approximate value Q _{es ti} of average quantization scale for each frame.

In step S35, the complexity calculating section 26 calculates the complexity based on the code amount (number of bits) B stored in the information buffer 24 and the calculated approximate value Q _esti of the average quantization scale for each frame. The approximate value X _{esti of the} chisity is converted to the approximate value Q of the average quantization scale.
_ESTI and product Q _{es ti} approximation B _ESTI code quantity (bit number)
X Calculate as _Besti .

In step S36, the MPEG4 image information encoding unit (I / P-VOP) 21 calculates a target code amount (target bit) according to the approximate value X _esti of the complexity.

[0130] Another example of the image information conversion apparatus is a compressed image analysis apparatus 8 as an example of the image information conversion apparatus shown in FIG. Since there is no need for parsing, the amount of calculation processing is reduced.

As described above, the MPEG2 image compression information (bit stream) has been used as the input, and the MPEG4 image compression information (bit stream) has been used as the output. However, the input and output are not limited to this.
H.263 or other image compression information (bit stream).

[0132]

As described above, the present invention provides MPEG2 image compression information (bit stream) for interlaced scanning.
Is input, and in each frame in the input MPEG2 image compression information (bit stream), an average quantization scale for the entire frame is approximately calculated using quantizer_scale_code which is information included in a slice header. Code amount allocation for each VOP with a smaller processing amount by using the approximate value of the complexity of each frame in the input MPEG2 image compression information (bit stream) calculated using the approximate value of the quantization scale Is optimized for the image,
It provides a means for converting into progressively scanned MPEG4 image compression information (bit stream) and outputting it.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an example of an image information processing apparatus.

FIG. 2 is a flowchart for performing code amount control using a complexity X;

FIG. 3 is a block diagram illustrating a configuration of another example of the image information processing apparatus.

FIG. 4 is a flowchart showing calculation of a target code amount (target bit) for a VOP.

FIG. 5 is a block diagram showing a configuration of a conventional image information conversion device.

FIG. 6 is a flowchart showing the operation principle of the code amount control method.

[Explanation of symbols]

7 picture type discriminator, 8 compression information analyzer, 9
MPEG2 image information decoding unit (I / P picture), 10
Thinning unit, 11 MPEG4 image information encoding unit (I /
P-VOP), 12 motion vector synthesizer, 13 motion vector detector

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Teruhiko Suzuki 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Yoichi Yagasaki 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation F term (reference) 5C059 KK41 LB05 LB07 MA00 MA03 MA05 MA13 MA23 MB01 MC11 NN01 PP05 PP06 PP07 RC14 RC28 SS10 TA60 TB05 TB18 TC04 TC06 TC10 TC18 TD03 TD16 UA02 UA34 5J064 AA02 BB01 BC25

Claims (15)

[Claims] An image information conversion apparatus for converting input image compression information of interlaced scanning compressed by a first compression encoding method into output image compression information of progressive scanning compressed by a second compression encoding method. In the above, using the quantization scale information included in a predetermined position of the input image compression information compressed by the first compression encoding method,
The approximate value of the average quantization scale of each frame of the input image compression information is obtained, and the approximate value of the complexity of the image of the frame is obtained using the approximate value and the code amount allocated to each frame. An image information conversion device comprising code amount control means for controlling a code amount in encoding of output image compression information based on a value. 2. A compression information analyzing means for analyzing the input image compression information and extracting at least a code amount allocated to each frame of the input image compression information, and storing the code amount and delaying for a predetermined period. 2. The image information conversion device according to claim 1, further comprising an information buffer for causing the image information to be converted. 3. The input image compression information and the output image compression information are configured in units of pixel blocks constituting a frame, the predetermined position is a header of a pixel block sequence, and the compression information analysis is performed. 3. The image information conversion apparatus according to claim 2, wherein said means comprises a header extracting means for extracting a header of said pixel block sequence. 4. Based on quantization scale information of each pixel block column and the number of pixel blocks included in a frame,
2. The image information conversion apparatus according to claim 1, wherein an approximate value of the average quantization scale for each frame is calculated by the following equation. (Equation 1) Here, the approximate value of the average quantization scale for each frame is Q _esti, and the quantization scale of the j-th pixel block sequence is
Let q_slice _j and the number of pixel blocks included in each frame be N _slice . 5. The image information conversion apparatus according to claim 4, wherein an approximate value of the complexity of each frame of the input image compression information is calculated by the following equation. (Equation 2) Here, the approximate value of the complexity for each frame is X _esti , the approximate value of the average quantization scale for each frame is Q _esti, and the allocated code amount for each frame is B
And 6. The first compression encoding method is MPEG.
2. The second compression encoding method is MPEG4, and VOP ₁ ,... VO corresponding to the image of the output image compression information
Picture information converting apparatus according to claim 5, wherein the target code amount R _1, characterized in that given by the following expression for VOP ₁ in the random accessible unit GOV composed of P _n. (Equation 3) Here, the code amount assigned to the entire image that has not been encoded by the GOV of the output image compression information is R, VOP ₁ ,
VOP _2, ... complexity of the approximate value X _{1_Esti} for _{VOP n,} X 2_exti, ... to the _X n_esti, the function whose variable is the complexity X _k and _{X l K (X k, X} l) and. 7. The image information conversion apparatus according to claim 6, wherein said function is given by the following equation. (Equation 4) 8. The image information conversion device according to claim 7, wherein the value of the exponent 1 / (1 + m) of the function is 0.6 to 1.2. 9. The image information conversion apparatus according to claim 7, wherein a value of an exponent 1 / (1 + m) of said function is set to 1.0. 10. The image information conversion apparatus according to claim 7, wherein the operation of the function is performed by referring to a table prepared in advance. 11. The image information conversion apparatus according to claim 6, wherein said function is given by the following equation. (Equation 5) Note that _Kp = 1.0 and _Kb = 1.4. 12. Decoding means for decoding the input image compression information, and rate conversion means for performing a rate conversion by thinning out the image information decoded by the decoding means,
The rate conversion means passes the forward coded image predicted and coded with reference to the forward direction in the intra coded image coded in the frame and the display order in the display order. 2. The image information conversion apparatus according to claim 1, wherein the bidirectionally predicted coded image that has been predictively coded by reference is discarded. 13. An image information conversion method for converting input image compression information of interlaced scanning compressed by a first compression encoding method into output image compression information of progressive scanning compressed by a second compression encoding method. In the above, using the quantization scale information included in a predetermined position of the input image compression information compressed by the first compression encoding method,
Obtaining an approximate value of the average quantization scale of each frame of the input image compression information; and obtaining an approximate value of the complexity of the image of the frame using the approximate value and the code amount allocated to each frame. And controlling a code amount in coding of the output image compression information based on the approximate value. 14. A step of analyzing the input image compression information to extract at least a code amount assigned to each frame of the input image compression information, storing the code amount in the information buffer, and extracting the code amount for a predetermined period. 14. The method according to claim 13, further comprising the step of delaying the input image compression information by delaying. 15. The input image compression information and the output image compression information are configured in units of pixel blocks constituting a frame, wherein the predetermined position is a header of a pixel block sequence, and the pixel block sequence is 15. The method according to claim 14, further comprising the step of:
The described image information conversion method.